Plants having altered agronomic characteristics under nitrogen limiting conditions and related constructs and methods involving genes encoding snf2 domain-containing polypeptides

ABSTRACT

Isolated polynucleotides and polypeptides and recombinant DNA constructs particularly useful for altering agronomic characteristics of plants under nitrogen limiting conditions, compositions (such as plants or seeds) comprising these recombinant DNA constructs, and methods utilizing these recombinant DNA constructs. The recombinant DNA construct comprises a polynucleotide operably linked to a promoter functional in a plant, wherein said polynucleotide encodes a SNF2 domain-containing polypeptide.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No. 13/259,582, filed Sep. 23, 2011, which is a 371 filing of PCT/US10/28773, filed Mar. 26, 2010, which claims the benefit of U.S. Provisional Application No. 61/163,887, filed Mar. 27, 2009, the entire content of which is herein incorporated by reference.

REFERENCE TO SEQUENCE LISTING SUBMITTED ELECTRONICALLY

The official copy of the sequence listing is submitted electronically via EFS-Web as an ASCII formatted sequence listing with a file named 20150609_BB1698USDIV_SequenceListing_ST25.txt created on Jun. 9, 2015 and having a size of 507 kilobytes and is filed concurrently with the specification. The sequence listing contained in this ASCII formatted document is part of the specification and is herein incorporated by reference in its entirety.

FIELD OF THE INVENTION

The field of invention relates to plant breeding and genetics and, in particular, relates to recombinant DNA constructs useful in plants for conferring nitrogen use efficiency and/or tolerance to nitrogen limiting conditions.

BACKGROUND OF THE INVENTION

Abiotic stressors significantly limit crop production worldwide. Cumulatively, these factors are estimated to be responsible for an average 70% reduction in agricultural production. Plants are sessile and have to adjust to the prevailing environmental conditions of their surroundings. This has led to their development of a great plasticity in gene regulation, morphogenesis, and metabolism. Adaptation and defense strategies involve the activation of genes encoding proteins important in the acclimation or defense towards the different stressors.

The absorption of nitrogen by plants plays an important role in their growth (Gallais et al., J. Exp. Bot. 55(396):295-306 (2004)). Plants synthesize amino acids from inorganic nitrogen in the environment. Consequently, nitrogen fertilization has been a powerful tool for increasing the yield of cultivated plants, such as maize and soybean. Today farmers desire to reduce the use of nitrogen fertilizer, in order to avoid pollution by nitrates and to maintain a sufficient profit margin. If the nitrogen assimilation capacity of a plant can be increased, then increases in plant growth and yield increase are also expected. In summary, plant varieties that have a better nitrogen use efficiency (NUE) are desirable.

Activation tagging can be utilized to identify genes with the ability to affect a trait. This approach has been used in the model plant species Arabidopsis thaliana (Weigel et al., Plant Physiol. 122:1003-1013 (2000)). Insertions of transcriptional enhancer elements can dominantly activate and/or elevate the expression of nearby endogenous genes. This method can be used to identify genes of interest for a particular trait (e.g. nitrogen use efficiency in a plant), genes that when placed in an organism as a transgene can alter that trait.

SUMMARY OF THE INVENTION

The present invention includes:

In one embodiment, a plant comprising in its genome a recombinant DNA construct comprising a polynucleotide operably linked to at least one regulatory element, wherein said polynucleotide encodes a polypeptide having an amino acid sequence of at least 50% sequence identity, based on the Clustal V method of alignment, when compared to SEQ ID NO:19, 21, 23, 25, 27, 29, 30, 31, 32, 36, 38, 40, 42, 44, 46, 48, or 49, and wherein said plant exhibits increased nitrogen stress tolerance when compared to a control plant not comprising said recombinant DNA construct.

In another embodiment, a plant comprising in its genome a recombinant DNA construct comprising a polynucleotide operably linked to at least one regulatory element, wherein said polynucleotide encodes a polypeptide having an amino acid sequence of at least 50% sequence identity, based on the Clustal V method of alignment, when compared to SEQ ID NO:19, 21, 23, 25, 27, 29, 30, 31, 32, 36, 38, 40, 42, 44, 46, 48, or 49, and wherein said plant exhibits an alteration of at least one agronomic characteristic when compared to a control plant not comprising said recombinant DNA construct. Optionally, the plant exhibits said alteration of said at least one agronomic characteristic when compared, under nitrogen limiting conditions, to said control plant not comprising said recombinant DNA construct. The at least one agronomic trait may be yield, biomass, or both, and the alteration may be an increase.

In another embodiment, the present invention includes any of the plants of the present invention wherein the plant is selected from the group consisting of: maize, soybean, sunflower, sorghum, canola, wheat, alfalfa, cotton, rice, barley, millet, sugar cane and switchgrass.

In another embodiment, the present invention includes seed of any of the plants of the present invention, wherein said seed comprises in its genome a recombinant DNA construct comprising a polynucleotide operably linked to at least one regulatory element, wherein said polynucleotide encodes a polypeptide having an amino acid sequence of at least 50% sequence identity, based on the Clustal V method of alignment, when compared to SEQ ID NO:19, 21, 23, 25, 27, 29, 30, 31, 32, 36, 38, 40, 42, 44, 46, 48, or 49, and wherein a plant produced from said seed exhibits either an increased nitrogen stress tolerance, or an alteration of at least one agronomic characteristic, or both, when compared to a control plant not comprising said recombinant DNA construct. The at least one agronomic trait may be yield, biomass, or both and the alteration may be an increase.

In another embodiment, a method of increasing nitrogen stress tolerance in a plant, comprising (a) introducing into a regenerable plant cell a recombinant DNA construct comprising a polynucleotide operably linked to at least one regulatory sequence, wherein the polynucleotide encodes a polypeptide having an amino acid sequence of at least 50% sequence identity, based on the Clustal V method of alignment, when compared to SEQ ID NO:19, 21, 23, 25, 27, 29, 30, 31, 32, 36, 38, 40, 42, 44, 46, 48, or 49; (b) regenerating a transgenic plant from the regenerable plant cell after step (a), wherein the transgenic plant comprises in its genome the recombinant DNA construct; and (c) obtaining a progeny plant derived from the transgenic plant of step (b), wherein said progeny plant comprises in its genome the recombinant DNA construct and exhibits increased nitrogen stress tolerance when compared to a control plant not comprising the recombinant DNA construct.

In another embodiment, a method of evaluating nitrogen stress tolerance in a plant, comprising (a) obtaining a transgenic plant, wherein the transgenic plant comprises in its genome a recombinant DNA construct comprising a polynucleotide operably linked to at least one regulatory sequence, wherein the polynucleotide encodes a polypeptide having an amino acid sequence of at least 50% sequence identity, based on the Clustal V method of alignment, when compared to SEQ ID NO:19, 21, 23, 25, 27, 29, 30, 31, 32, 36, 38, 40, 42, 44, 46, 48, or 49; (b) obtaining a progeny plant derived from the transgenic plant, wherein the progeny plant comprises in its genome the recombinant DNA construct; and (c) evaluating the progeny plant for nitrogen stress tolerance compared to a control plant not comprising the recombinant DNA construct.

In another embodiment, a method of determining an alteration of an agronomic characteristic in a plant, comprising (a) obtaining a transgenic plant, wherein the transgenic plant comprises in its genome a recombinant DNA construct comprising a polynucleotide operably linked to at least one regulatory sequence, wherein the polynucleotide encodes a polypeptide having an amino acid sequence of at least 50% sequence identity, based on the Clustal V method of alignment, when compared to SEQ ID NO:19, 21, 23, 25, 27, 29, 30, 31, 32, 36, 38, 40, 42, 44, 46, 48, or 49, wherein the transgenic plant comprises in its genome the recombinant DNA construct; (b) obtaining a progeny plant derived from the transgenic plant, wherein the progeny plant comprises in its genome the recombinant DNA construct; and (c) determining whether the progeny plant exhibits an alteration of at least one agronomic characteristic when compared to a control plant not comprising the recombinant DNA construct. Optionally, said determining step (c) comprises determining whether the transgenic plant exhibits an alteration of at least one agronomic characteristic when compared, under nitrogen limiting conditions, to a control plant not comprising the recombinant DNA construct. The at least one agronomic trait may be yield, biomass, or both and the alteration may be an increase.

In another embodiment, the present invention includes any of the methods of the present invention wherein the plant is selected from the group consisting of: maize, soybean, sunflower, sorghum, canola, wheat, alfalfa, cotton, rice, barley, millet, sugar cane and switchgrass.

In another embodiment, the present invention includes an isolated polynucleotide comprising: (a) a nucleotide sequence encoding a SNF2-domain containing polypeptide, wherein the polypeptide has an amino acid sequence of at least 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95% sequence identity, based on the Clustal V method of alignment, when compared to SEQ ID NO:19, 21, 23, 36, 38, or 46, or (b) a full complement of the nucleotide sequence, wherein the full complement and the nucleotide sequence consist of the same number of nucleotides and are 100% complementary. The polypeptide may comprise the amino acid sequence of SEQ ID NO:19, 21, 23, 36, 38, or 46. The nucleotide sequence may comprise the nucleotide sequence of SEQ ID NO:18, 20, 22, 35, 37, or 45.

In another embodiment, the present invention concerns a recombinant DNA construct comprising any of the isolated polynucleotides of the present invention operably linked to at least one regulatory sequence, and a cell, a plant, and a seed comprising the recombinant DNA construct. The cell may be eukaryotic, e.g., a yeast, insect or plant cell, or prokaryotic, e.g., a bacterial cell.

BRIEF DESCRIPTION OF THE DRAWINGS AND SEQUENCE LISTINGS

The invention can be more fully understood from the following detailed description and the accompanying drawings and Sequence Listing which form a part of this application.

FIG. 1 shows a schematic of the pHSbarENDs2 activation tagging construct used to make the Arabidopsis populations (SEQ ID NO:1).

FIG. 2 shows a schematic of the vector pDONR™Zeo (SEQ ID NO:2), GATEWAY® donor vector. The attP1 site is at nucleotides 570-801; the attP2 site is at nucleotides 2754-2985 (complementary strand).

FIG. 3 shows a schematic of the vector pDONR™221 (SEQ ID NO:3), GATEWAY® donor vector. The attP1 site is at nucleotides 570-801; the attP2 site is at nucleotides 2754-2985 (complementary strand).

FIG. 4 shows a schematic of the vector pBC-yellow (SEQ ID NO:4), a destination vector for use in construction of expression vectors for Arabidopsis. The attR1 site is at nucleotides 11276-11399 (complementary strand); the attR2 site is at nucleotides 9695-9819 (complementary strand).

FIG. 5 shows a schematic of the vector PHP27840 (SEQ ID NO:5), a destination vector for use in construction of expression vectors for soybean. The attR1 site is at nucleotides 7310-7434; the attR2 site is at nucleotides 8890-9014.

FIG. 6 shows a schematic of the vector PHP23236 (SEQ ID NO:6), a destination vector for use in construction of expression vectors for Gaspe Flint derived maize lines. The attR1 site is at nucleotides 2006-2130; the attR2 site is at nucleotides 2899-3023.

FIG. 7 shows a schematic of the vector PHP10523 (SEQ ID NO:7), a plasmid DNA present in Agrobacterium strain LBA4404 (Komari et al., Plant J. 10:165-174 (1996); NCBI General Identifier No. 59797027).

FIG. 8 shows a schematic of the vector PHP23235 (SEQ ID NO:8), a vector used to construct the destination vector PHP23236.

FIG. 9 shows a schematic of the vector PHP20234 (SEQ ID NO:9).

FIG. 10 shows a schematic of the destination vector PHP22655 (SEQ ID NO:10).

FIG. 11 shows a schematic of the destination vector PHP29634 (SEQ ID NO:15), used in construction of expression vectors for Gaspe Flint derived maize lines.

FIG. 12 shows a typical grid pattern for five lines (labeled 1 through 5—eleven individuals for each line), plus wild-type control C1 (nine individuals), used in screens.

FIG. 13 shows a graph showing the effect of several different potassium nitrate concentrations on plant color as determined by image analysis. The response of the green color bin (hues 50 to 66) to nitrate dosage demonstrates that this bin can be used as an indicator of nitrogen assimilation.

FIG. 14 shows the growth medium used for semi-hydroponics maize growth in Example 18.

FIG. 15 shows a chart setting forth data relating to the effect of different nitrate concentrations on the growth and development of Gaspe Flint derived maize lines in Example 18.

FIGS. 16A-AM show the multiple alignment of the full length amino acid sequences of the Arabidopsis thaliana SNF2 domain-containing polypeptides (SEQ ID NOs:25, 27, and 29) and their homologs (SEQ ID NOs: 19, 21, 23, 30, 31, 32, 36, 38, 40, 42, 44, 46, 48, and 49).

FIG. 17 shows a chart of the percent sequence identity and the divergence values for each pair of amino acids sequences displayed in FIGS. 16A-AM.

The sequence descriptions and Sequence Listing attached hereto comply with the rules governing nucleotide and/or amino acid sequence disclosures in patent applications as set forth in 37 C.F.R. §1.821-1.825. The Sequence Listing contains the one letter code for nucleotide sequence characters and the three letter codes for amino acids as defined in conformity with the IUPAC-IUBMB standards described in Nucleic Acids Res. 13:3021-3030 (1985) and in the Biochemical J. 219 (2):345-373 (1984) which are herein incorporated by reference. The symbols and format used for nucleotide and amino acid sequence data comply with the rules set forth in 37 C.F.R. §1.822.

Table 1 lists certain polypeptides that are described herein, the designation of the cDNA clones that comprise the nucleic acid fragments encoding polypeptides representing all or a substantial portion of these polypeptides, and the corresponding identifier (SEQ ID NO:) as used in the attached Sequence Listing.

TABLE 1 SNF2 domain-containing polypeptides SEQ ID NO: Clone Designation Amino (if applicable) Species Nucleotide Acid SNF2 domain- cfp1n.pk008.f7:fis Zea mays 18 19 containing protein SNF2 domain- cfp4n.pk061.o18:fis Zea mays 20 21 containing protein SNF2 domain- contig of: Zea mays 22 23 containing protein p0016.ctsca12r SNF2 domain- N/A Eragrostis 35 36 containing protein nindensis SNF2 domain- N/A Paspalum 37 38 containing protein notatum

SEQ ID NO:1 is the nucleotide sequence of the pHSbarENDs2 activation tagging vector (FIG. 1).

SEQ ID NO:2 is the nucleotide sequence of the pDONR™Zeo construct (FIG. 2).

SEQ ID NO:3 is the nucleotide sequence of the pDONR™221 construct (FIG. 3).

SEQ ID NO:4 is the nucleotide sequence of the pBC-yellow vector (FIG. 4).

SEQ ID NO:5 is the nucleotide sequence of the PHP27840 vector (FIG. 5).

SEQ ID NO:6 is the nucleotide sequence of the destination vector PHP23236 (FIG. 6).

SEQ ID NO:7 is the nucleotide sequence of the PHP10523 vector (FIG. 7).

SEQ ID NO:8 is the nucleotide sequence of the PHP23235 vector (FIG. 8).

SEQ ID NO:9 is the nucleotide sequence of the PHP20234 vector (FIG. 9).

SEQ ID NO:10 is the nucleotide sequence of the destination vector PHP22655 (FIG. 10).

SEQ ID NO:11 is the nucleotide sequence of the poly-linker used to substitute the Pacl restriction site at position 5775 of pHSbarENDs2.

SEQ ID NO:12 is the nucleotide sequence of the attB1 sequence.

SEQ ID NO:13 is the nucleotide sequence of the attB2 sequence.

SEQ ID NO:14 is the nucleotide sequence of the entry clone PHP23112.

SEQ ID NO:15 is the nucleotide sequence of the PHP29634 vector (FIG. 11).

SEQ ID NO:16 is the forward primer VC062.

SEQ ID NO:17 is the reverse primer VC063.

SEQ ID NOs:18-23 (see Table 1).

SEQ ID NO:24 is the nucleotide sequence of the gene that encodes the Arabidopsis thaliana SNF domain-containing protein, variant 1 (SNF2.1) (At1g61140.1; NCBI General Identifier No. 186492169).

SEQ ID NO:25 is the amino acid sequence of the Arabidopsis thaliana SNF domain-containing protein, variant 1 (referred to herein as SNF2.1) (At1g61140.1; NCBI General Identifier No. 186492170).

SEQ ID NO:26 is the nucleotide sequence of the gene that encodes the Arabidopsis thaliana SNF domain-containing protein, variant 2 (SNF2.2) (At1g61140.2; NCBI General Identifier No. 186492171).

SEQ ID NO:27 is the amino acid sequence of the Arabidopsis thaliana SNF domain-containing protein, variant 2 (referred to herein as SNF2.2) (At1g61140.2; NCBI General Identifier No. 186492172).

SEQ ID NO:28 is the nucleotide sequence of the gene that encodes the Arabidopsis thaliana SNF domain-containing protein, variant 3 (SNF2.3) (At1g61140.3; NCBI General Identifier No. 186492174).

SEQ ID NO:29 is the amino acid sequence of the Arabidopsis thaliana SNF domain-containing protein, variant 3 (referred to herein as SNF2.3) (At1g61140.3; NCBI General Identifier No. 186492175).

SEQ ID NO:30 is the amino acid sequence of the Oryza sativa putative ATPase protein (NCBI General Identifier No. 53792213).

SEQ ID NO:31 is the amino acid sequence of the Oryza sativa hypothetical protein OsI_(—)28047 (NCBI General Identifier No. 218200575).

SEQ ID NO:32 is the amino acid sequence of the Oryza sativa protein (General Identifier No. 90399293).

SEQ ID NO:33 is the nucleotide sequence of the At1g61140.1-5′ attB forward primer.

SEQ ID NO:34 is the nucleotide sequence of the At1g61140.1-3′ attB reverse primer.

SEQ ID NOs:35-38 (see Table 1).

SEQ ID NO:39 is the nucleotide sequence of the At1g61140.1 gene (transcript identifier 47522 on the phytozome website) from Arabidopsis lyrata.

SEQ ID NO:40 is the amino acid sequence of the protein encoded by SEQ ID NO:39.

SEQ ID NO:41 is the nucleotide sequence of the At1g11100.1 gene (transcript identifier 471244 on the phytozome website) from Arabidopsis lyrata.

SEQ ID NO:42 is the amino acid sequence of the protein encoded by SEQ ID NO:41.

SEQ ID NO:43 is the FGENESH prediction of a SNF2 domain-containing Zea mays gene on public BAC c0566n04.

SEQ ID NO:44 is the amino acid sequence of the protein encoded by SEQ ID NO:43.

SEQ ID NO:45 is a manually edited version of SEQ ID NO:43 in which SEQ ID NO:43 was aligned with sequences from other species and manually edited to remove putative introns.

SEQ ID NO:46 is the amino acid sequence of the protein encoded by SEQ ID NO:45.

SEQ ID NO:47 is the nucleotide sequence of the Oryza sativa locus Os01g57110.2, a SNF2 family N-terminal domain containing protein.

SEQ ID NO:48 is the amino acid sequence of the protein encoded by SEQ ID NO:49.

SEQ ID NO:49 is the amino acid sequence of the Sorghum bicolor hypothetical protein (locus Sb03g036380; NCBI GI No. 242058897).

DETAILED DESCRIPTION

The disclosure of each reference set forth herein is hereby incorporated by reference in its entirety.

As used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural reference unless the context clearly dictates otherwise. Thus, for example, reference to “a plant” includes a plurality of such plants, reference to “a cell” includes one or more cells and equivalents thereof known to those skilled in the art, and so forth.

As Used Herein:

The terms “monocot” and “monocotyledonous plant” are used interchangeably herein. A monocot of the current invention includes the Gramineae.

The terms “dicot” and “dicotyledonous plant” are used interchangeably herein. A dicot of the current invention includes the following families: Brassicaceae, Leguminosae, and Solanaceae.

The terms “full complement” and “full-length complement” are used interchangeably herein, and refer to a complement of a given nucleotide sequence, wherein the complement and the nucleotide sequence consist of the same number of nucleotides and are 100% complementary.

A “trait” refers to a physiological, morphological, biochemical, or physical characteristic of a plant or particular plant material or cell. In some instances, this characteristic is visible to the human eye, such as seed or plant size, or can be measured by biochemical techniques, such as detecting the protein, starch, or oil content of seed or leaves, or by observation of a metabolic or physiological process, e.g. by measuring tolerance to water deprivation or particular salt or sugar concentrations, or by the observation of the expression level of a gene or genes, or by agricultural observations such as osmotic stress tolerance or yield.

“Nitrogen limiting conditions” refers to conditions where the amount of total available nitrogen (e.g., from nitrates, ammonia, or other known sources of nitrogen) is not sufficient to sustain optimal plant growth and development. One skilled in the art would recognize conditions where total available nitrogen is sufficient to sustain optimal plant growth and development. One skilled in the art would recognize what constitutes sufficient amounts of total available nitrogen, and what constitutes soils, media and fertilizer inputs for providing nitrogen to plants. Nitrogen limiting conditions will vary depending upon a number of factors, including but not limited to, the particular plant and environmental conditions.

“Agronomic characteristic” is a measurable parameter including but not limited to, greenness, yield, growth rate, biomass, fresh weight at maturation, dry weight at maturation, fruit yield, seed yield, total plant nitrogen content, fruit nitrogen content, seed nitrogen content, nitrogen content in vegetative tissue, whole plant amino acid content, vegetative tissue free amino acid content, fruit free amino acid content, seed free amino acid content, total plant protein content, fruit protein content, seed protein content, protein content in a vegetative tissue, drought tolerance, nitrogen uptake, resistance to root lodging, harvest index, stalk lodging, plant height, ear height, ear length, salt tolerance, early seedling vigor, and seedling emergence under low temperature stress.

Increased biomass can be measured, for example, as an increase in plant height, plant total leaf area, plant fresh weight, plant dry weight or plant seed yield, as compared with control plants.

The ability to increase the biomass or size of a plant would have several important commercial applications. Crop species may be generated that produce larger cultivars, generating higher yield in, for example, plants in which the vegetative portion of the plant is useful as food, biofuel or both.

Increased leaf size may be of particular interest. Increasing leaf biomass can be used to increase production of plant-derived pharmaceutical or industrial products. An increase in total plant photosynthesis is typically achieved by increasing leaf area of the plant. Additional photosynthetic capacity may be used to increase the yield derived from particular plant tissue, including the leaves, roots, fruits or seed, or permit the growth of a plant under decreased light intensity or under high light intensity.

Modification of the biomass of another tissue, such as root tissue, may be useful to improve a plant's ability to grow under harsh environmental conditions, including drought or nutrient deprivation, because larger roots may better reach water or nutrients or take up water or nutrients.

For some ornamental plants, the ability to provide larger varieties would be highly desirable. For many plants, including fruit-bearing trees, trees that are used for lumber production, or trees and shrubs that serve as view or wind screens, increased stature provides improved benefits in the forms of greater yield or improved screening.

“Harvest index” refers to the grain weight divided by the total plant weight.

“SNF2 domains” are found in ATP-dependent chromatin remodeling proteins involved in transcriptional control, DNA repair, and recombination. They contain seven conserved sequence motifs found in the superfamily II of DNA/RNA helicases.

Genes encoding SNF2 domain-containing proteins include without limitation the three variants of the Arabidopsis thaliana gene locus At1g61140 (SEQ ID NOs: 24, 26, and 28), referred to herein as snf2.1, snf2.2, and snf2.3, respectively, and the nucleotide homologs from other plant species, including, but not limited to, Zea mays, Arabidopsis lyrata, Eragrostis nindensis (Resurrection grass), Paspalum notatum (Bahiagrass), and Oryza sativa (SEQ ID NOs:18, 20, 22, 35, 37, 39, 41, 43, 45, and 47).

SNF2 domain-containing proteins include without limitation the proteins encoded by SEQ ID NOs:24, 26, and 28 (and referred to herein as SNF2.1, SNF2.2, and SNF2.3, respectively), and the protein homologs from other plant species, including, but not limited to, Zea mays, Arabidopsis lyrata, Eragrostis nindensis (Resurrection grass), Paspalum notatum (Bahiagrass), Oryza sativa, and Sorghum bicolor (SEQ ID NOs: 19, 21, 23, 30, 31, 32, 36, 38, 40, 42, 44, 46, 48, and 49).

“Splice variants” used herein refers to alternative forms of RNA transcribed from a gene. Splice variation naturally occurs as a result of alternative sites being spliced within a single transcribed RNA molecule or between separately transcribed RNA molecules, and may result in several different forms of mRNA transcribed from the same gene. Thus, splice variants may encode polypeptides having different amino acid sequences, which may or may not have similar functions in the organism.

“Nitrogen stress tolerance” is a trait of a plant and refers to the ability of the plant to survive under nitrogen limiting conditions.

“Increased nitrogen stress tolerance” of a plant is measured relative to a reference or control plant, and means that the nitrogen stress tolerance of the plant is increased by any amount or measure when compared to the nitrogen stress tolerance of the reference or control plant.

A “nitrogen stress tolerant plant” is a plant that exhibits nitrogen stress tolerance. A nitrogen stress tolerant plant may be a plant that exhibits an increase in at least one agronomic characteristic relative to a control plant under nitrogen limiting conditions.

“Environmental conditions” refer to conditions under which the plant is grown, such as the availability of water, availability of nutrients (for example nitrogen), or the presence of insects or disease.

“Transgenic” refers to any cell, cell line, callus, tissue, plant part or plant, the genome of which has been altered by the presence of a heterologous nucleic acid, such as a recombinant DNA construct, including those initial transgenic events as well as those created by sexual crosses or asexual propagation from the initial transgenic event. The term “transgenic” as used herein does not encompass the alteration of the genome (chromosomal or extra-chromosomal) by conventional plant breeding methods or by naturally occurring events such as random cross-fertilization, non-recombinant viral infection, non-recombinant bacterial transformation, non-recombinant transposition, or spontaneous mutation.

“Genome” as it applies to plant cells encompasses not only chromosomal DNA found within the nucleus, but organelle DNA found within subcellular components (e.g., mitochondrial, plastid) of the cell.

“Plant” includes reference to whole plants, plant organs, plant tissues, seeds and plant cells and progeny of same. Plant cells include, without limitation, cells from seeds, suspension cultures, embryos, meristematic regions, callus tissue, leaves, roots, shoots, gametophytes, sporophytes, pollen, and microspores.

“Progeny” comprises any subsequent generation of a plant.

“Transgenic plant” includes reference to a plant which comprises within its genome a heterologous polynucleotide. For example, the heterologous polynucleotide is stably integrated within the genome such that the polynucleotide is passed on to successive generations. The heterologous polynucleotide may be integrated into the genome alone or as part of a recombinant DNA construct.

“Heterologous” with respect to sequence means a sequence that originates from a foreign species, or, if from the same species, is substantially modified from its native form in composition and/or genomic locus by deliberate human intervention.

“Polynucleotide”, “nucleic acid sequence”, “nucleotide sequence”, or “nucleic acid fragment” are used interchangeably to refer to a polymer of RNA or DNA that is single- or double-stranded, optionally containing synthetic, non-natural or altered nucleotide bases. Nucleotides (usually found in their 5′-monophosphate form) are referred to by their single letter designation as follows: “A” for adenylate or deoxyadenylate (for RNA or DNA, respectively), “C” for cytidylate or deoxycytidylate, “G” for guanylate or deoxyguanylate, “U” for uridylate, “T” for deoxythymidylate, “R” for purines (A or G), “Y” for pyrimidines (C or T), “K” for G or T, “H” for A or C or T, “I” for inosine, and “N” for any nucleotide.

“Polypeptide”, “peptide”, “amino acid sequence” and “protein” are used interchangeably herein to refer to a polymer of amino acid residues. The terms apply to amino acid polymers in which one or more amino acid residue is an artificial chemical analogue of a corresponding naturally occurring amino acid, as well as to naturally occurring amino acid polymers. The terms “polypeptide”, “peptide”, “amino acid sequence”, and “protein” are also inclusive of modifications including, but not limited to, glycosylation, lipid attachment, sulfation, gamma-carboxylation of glutamic acid residues, hydroxylation and ADP-ribosylation.

“Messenger RNA (mRNA)” refers to the RNA that is without introns and that can be translated into protein by the cell.

“cDNA” refers to a DNA that is complementary to and synthesized from an mRNA template using the enzyme reverse transcriptase. The cDNA can be single-stranded or converted into the double-stranded form using the Klenow fragment of DNA polymerase I.

An “Expressed Sequence Tag” (“EST”) is a DNA sequence derived from a cDNA library and therefore is a sequence which has been transcribed. An EST is typically obtained by a single sequencing pass of a cDNA insert. The sequence of an entire cDNA insert is termed the “Full-Insert Sequence” (“FIS”). A “Contig” sequence is a sequence assembled from two or more sequences that can be selected from, but not limited to, the group consisting of an EST, FIS and PCR sequence. A sequence encoding an entire or functional protein is termed a “Complete Gene Sequence” (“CGS”) and can be derived from an FIS or a contig.

“Mature” protein refers to a post-translationally processed polypeptide; i.e., one from which any pre- or pro-peptides present in the primary translation product have been removed.

“Precursor” protein refers to the primary product of translation of mRNA; i.e., with pre- and pro-peptides still present. Pre- and pro-peptides may be and are not limited to intracellular localization signals.

“Isolated” refers to materials, such as nucleic acid molecules and/or proteins, which are substantially free or otherwise removed from components that normally accompany or interact with the materials in a naturally occurring environment. Isolated polynucleotides may be purified from a host cell in which they naturally occur. Conventional nucleic acid purification methods known to skilled artisans may be used to obtain isolated polynucleotides. The term also embraces recombinant polynucleotides and chemically synthesized polynucleotides.

“Recombinant” refers to an artificial combination of two otherwise separated segments of sequence, e.g., by chemical synthesis or by the manipulation of isolated segments of nucleic acids by genetic engineering techniques. “Recombinant” also includes reference to a cell or vector, that has been modified by the introduction of a heterologous nucleic acid or a cell derived from a cell so modified, but does not encompass the alteration of the cell or vector by naturally occurring events (e.g., spontaneous mutation, natural transformation/transduction/transposition) such as those occurring without deliberate human intervention.

“Recombinant DNA construct” refers to a combination of nucleic acid fragments that are not normally found together in nature. Accordingly, a recombinant DNA construct may comprise regulatory sequences and coding sequences that are derived from different sources, or regulatory sequences and coding sequences derived from the same source, but arranged in a manner different than that normally found in nature.

The terms “entry clone” and “entry vector” are used interchangeably herein.

“Regulatory sequences” and “regulatory elements” are used interchangeably and refer to nucleotide sequences located upstream (5′ non-coding sequences), within, or downstream (3′ non-coding sequences) of a coding sequence, and which influence the transcription, RNA processing or stability, or translation of the associated coding sequence. Regulatory sequences may include, but are not limited to, promoters, translation leader sequences, introns, and polyadenylation recognition sequences.

“Promoter” refers to a nucleic acid fragment capable of controlling transcription of another nucleic acid fragment.

“Promoter functional in a plant” is a promoter capable of controlling transcription in plant cells whether or not its origin is from a plant cell.

“Tissue-specific promoter” and “tissue-preferred promoter” are used interchangeably to refer to a promoter that is expressed predominantly but not necessarily exclusively in one tissue or organ, but that may also be expressed in one specific cell.

“Developmentally regulated promoter” refers to a promoter whose activity is determined by developmental events.

“Operably linked” refers to the association of nucleic acid fragments in a single fragment so that the function of one is regulated by the other. For example, a promoter is operably linked with a nucleic acid fragment when it is capable of regulating the transcription of that nucleic acid fragment.

“Expression” refers to the production of a functional product. For example, expression of a nucleic acid fragment may refer to transcription of the nucleic acid fragment (e.g., transcription resulting in mRNA or functional RNA) and/or translation of mRNA into a precursor or mature protein.

“Phenotype” means the detectable characteristics of a cell or organism.

“Introduced” in the context of inserting a nucleic acid fragment (e.g., a recombinant DNA construct) into a cell, means “transfection” or “transformation” or “transduction” and includes reference to the incorporation of a nucleic acid fragment into a eukaryotic or prokaryotic cell where the nucleic acid fragment may be incorporated into the genome of the cell (e.g., chromosome, plasmid, plastid or mitochondrial DNA), converted into an autonomous replicon, or transiently expressed (e.g., transfected mRNA).

A “transformed cell” is any cell into which a nucleic acid fragment (e.g., a recombinant DNA construct) has been introduced.

“Transformation” as used herein refers to both stable transformation and transient transformation.

“Stable transformation” refers to the introduction of a nucleic acid fragment into a genome of a host organism resulting in genetically stable inheritance. Once stably transformed, the nucleic acid fragment is stably integrated in the genome of the host organism and any subsequent generation.

“Transient transformation” refers to the introduction of a nucleic acid fragment into the nucleus, or DNA-containing organelle, of a host organism resulting in gene expression without genetically stable inheritance.

“Allele” is one of several alternative forms of a gene occupying a given locus on a chromosome. When the alleles present at a given locus on a pair of homologous chromosomes in a diploid plant are the same that plant is homozygous at that locus. If the alleles present at a given locus on a pair of homologous chromosomes in a diploid plant differ that plant is heterozygous at that locus. If a transgene is present on one of a pair of homologous chromosomes in a diploid plant that plant is hemizygous at that locus.

A “chloroplast transit peptide” is an amino acid sequence which is translated in conjunction with a protein and directs the protein to the chloroplast or other plastid types present in the cell in which the protein is made. “Chloroplast transit sequence” refers to a nucleotide sequence that encodes a chloroplast transit peptide. A “signal peptide” is an amino acid sequence which is translated in conjunction with a protein and directs the protein to the secretory system (Chrispeels (1991) Ann. Rev. Plant Phys. Plant Mol. Biol. 42:21-53). If the protein is to be directed to a vacuole, a vacuolar targeting signal (supra) can further be added, or if to the endoplasmic reticulum, an endoplasmic reticulum retention signal (supra) may be added. If the protein is to be directed to the nucleus, any signal peptide present should be removed and instead a nuclear localization signal included (Raikhel (1992) Plant Phys. 100:1627-1632). A “mitochondrial signal peptide” is an amino acid sequence which directs a precursor protein into the mitochondria (Zhang and Glaser (2002) Trends Plant Sci 7:14-21).

Sequence alignments and percent identity calculations may be determined using a variety of comparison methods designed to detect homologous sequences including, but not limited to, the MEGALIGN® program of the LASERGENE® bioinformatics computing suite (DNASTAR® Inc., Madison, Wis.). Unless stated otherwise, multiple alignment of the sequences provided herein were performed using the Clustal V method of alignment (Higgins and Sharp, CABIOS. 5:151-153 (1989)) with the default parameters (GAP PENALTY=10, GAP LENGTH PENALTY=10). Default parameters for pairwise alignments and calculation of percent identity of protein sequences using the Clustal V method are KTUPLE=1, GAP PENALTY=3, WINDOW=5 and DIAGONALS SAVED=5. For nucleic acids these parameters are KTUPLE=2, GAP PENALTY=5, WINDOW=4 and DIAGONALS SAVED=4. After alignment of the sequences, using the Clustal V program, it is possible to obtain “percent identity” and “divergence” values by viewing the “sequence distances” table on the same program; unless stated otherwise, percent identities and divergences provided and claimed herein were calculated in this manner.

Standard recombinant DNA and molecular cloning techniques used herein are well known in the art and are described more fully in Sambrook, J., Fritsch, E. F. and Maniatis, T. Molecular Cloning: A Laboratory Manual; Cold Spring Harbor Laboratory Press: Cold Spring Harbor, 1989 (hereinafter “Sambrook”).

Turning Now to the Embodiments:

Embodiments include isolated polynucleotides and polypeptides, recombinant DNA constructs, compositions (such as plants or seeds) comprising these recombinant DNA constructs, and methods utilizing these recombinant DNA constructs.

Isolated Polynucleotides and Polypeptides

The present invention includes the following isolated polynucleotides and polypeptides:

An isolated polynucleotide comprising: (i) a nucleic acid sequence encoding a polypeptide having an amino acid sequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity, based on the Clustal V method of alignment, when compared to SEQ ID NO:19, 21, 23, 36, 38, or 46; or (ii) a full complement of the nucleic acid sequence of (i), wherein the full complement and the nucleic acid sequence of (i) consist of the same number of nucleotides and are 100% complementary. Any of the foregoing isolated polynucleotides may be utilized in any recombinant DNA constructs (including suppression DNA constructs) of the present invention. The polypeptide is a SNF2 domain-containing protein.

An isolated polypeptide having an amino acid sequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity, based on the Clustal V method of alignment, when compared to SEQ ID NO:19, 21, 23, 36, 38, or 46. The polypeptide is a SNF2 domain-containing protein.

An isolated polynucleotide comprising (i) a nucleic acid sequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity, based on the Clustal V method of alignment, when compared to SEQ ID NO:18, 20, 22, 35, 37, or 45; or (ii) a full complement of the nucleic acid sequence of (i). Any of the foregoing isolated polynucleotides may be utilized in any recombinant DNA constructs (including suppression DNA constructs) of the present invention. The isolated polynucleotide encodes a SNF2 domain-containing protein.

Recombinant DNA Constructs and Suppression DNA Constructs

In one aspect, the present invention includes recombinant DNA constructs (including suppression DNA constructs).

In one embodiment, a recombinant DNA construct comprises a polynucleotide operably linked to at least one regulatory sequence (e.g., a promoter functional in a plant), wherein the polynucleotide comprises (i) a nucleic acid sequence encoding an amino acid sequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity, based on the Clustal V method of alignment, when compared to SEQ ID NO:19, 21, 23, 25, 27, 29, 30, 31, 32, 36, 38, 40, 42, 44, 46, 48, or 49; or (ii) a full complement of the nucleic acid sequence of (i).

In another embodiment, a recombinant DNA construct comprises a polynucleotide operably linked to at least one regulatory sequence (e.g., a promoter functional in a plant), wherein said polynucleotide comprises (i) a nucleic acid sequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity, based on the Clustal V method of alignment, when compared to SEQ ID NO:18, 20, 22, 24, 26, 28, 35, 37, 39, 41, 43, 45, or 47; or (ii) a full complement of the nucleic acid sequence of (i).

In another embodiment, a recombinant DNA construct comprises a polynucleotide operably linked to at least one regulatory sequence (e.g., a promoter functional in a plant), wherein said polynucleotide encodes a SNF2 domain-containing protein.

In another aspect, the present invention includes suppression DNA constructs.

A suppression DNA construct can comprise at least one regulatory sequence (for example, a promoter functional in a plant) operably linked to (a) all or part of: (i) a nucleic acid sequence encoding a polypeptide having an amino acid sequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity, based on the Clustal V method of alignment, when compared to SEQ ID NO:19, 21, 23, 25, 27, 29, 30, 31, 32, 36, 38, 40, 42, 44, 46, 48, or 49; or (ii) a full complement of the nucleic acid sequence of (a)(i); or (b) a region derived from all or part of a sense strand or antisense strand of a target gene of interest, said region having a nucleic acid sequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity, based on the Clustal V method of alignment, when compared to said all or part of a sense strand or antisense strand from which said region is derived, and wherein said target gene of interest encodes a SNF2 domain-containing protein; or (c) all or part of: (i) a nucleic acid sequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity, based on the Clustal V method of alignment, when compared to SEQ ID NO:18, 20, 22, 24, 26, 28, 35, 37, 39, 41, 43, 45, or 47; or (ii) a full complement of the nucleic acid sequence of (c)(i). The suppression DNA construct may comprise a cosuppression construct, antisense construct, viral-suppression construct, hairpin suppression construct, stem-loop suppression construct, double-stranded RNA-producing construct, RNAi construct, or small RNA construct (e.g., an siRNA construct or an miRNA construct).

It is understood, as those skilled in the art will appreciate, that the invention encompasses more than the specific exemplary sequences. Alterations in a nucleic acid fragment which result in the production of a chemically equivalent amino acid at a given site, but do not affect the functional properties of the encoded polypeptide, are well known in the art. For example, a codon for the amino acid alanine, a hydrophobic amino acid, may be substituted by a codon encoding another less hydrophobic residue, such as glycine, or a more hydrophobic residue, such as valine, leucine, or isoleucine. Similarly, changes which result in substitution of one negatively charged residue for another, such as aspartic acid for glutamic acid, or one positively charged residue for another, such as lysine for arginine, can also be expected to produce a functionally equivalent product. Nucleotide changes which result in alteration of the N-terminal and C-terminal portions of the polypeptide molecule would also not be expected to alter the activity of the polypeptide. Each of the proposed modifications is well within the routine skill in the art, as is determination of retention of biological activity of the encoded products.

“Suppression DNA construct” is a recombinant DNA construct which when transformed or stably integrated into the genome of the plant, results in “silencing” of a target gene in the plant. The target gene may be endogenous or transgenic to the plant. “Silencing,” as used herein with respect to the target gene, refers generally to the suppression of levels of mRNA or protein/enzyme expressed by the target gene, and/or the level of the enzyme activity or protein functionality. The terms “suppression”, “suppressing” and “silencing”, used interchangeably herein, includes lowering, reducing, declining, decreasing, inhibiting, eliminating or preventing. “Silencing” or “gene silencing” does not specify mechanism and is inclusive, and not limited to, anti-sense, cosuppression, viral-suppression, hairpin suppression, stem-loop suppression, RNAi-based approaches, and small RNA-based approaches.

A suppression DNA construct may comprise a region derived from a target gene of interest and may comprise all or part of the nucleic acid sequence of the sense strand (or antisense strand) of the target gene of interest. Depending upon the approach to be utilized, the region may be 100% identical or less than 100% identical (e.g., at least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identical) to all or part of the sense strand (or antisense strand) of the gene of interest.

Suppression DNA constructs are well-known in the art, are readily constructed once the target gene of interest is selected, and include, without limitation, cosuppression constructs, antisense constructs, viral-suppression constructs, hairpin suppression constructs, stem-loop suppression constructs, double-stranded RNA-producing constructs, and more generally, RNAi (RNA interference) constructs and small RNA constructs such as sRNA (short interfering RNA) constructs and miRNA (microRNA) constructs.

“Antisense inhibition” refers to the production of antisense RNA transcripts capable of suppressing the expression of the target gene or gene product. “Antisense RNA” refers to an RNA transcript that is complementary to all or part of a target primary transcript or mRNA and that blocks the expression of a target isolated nucleic acid fragment (U.S. Pat. No. 5,107,065). The complementarity of an antisense RNA may be with any part of the specific gene transcript, i.e., at the 5′ non-coding sequence, 3′ non-coding sequence, introns, or the coding sequence.

“Cosuppression” refers to the production of sense RNA transcripts capable of suppressing the expression of the target gene or gene product. “Sense” RNA refers to RNA transcript that includes the mRNA and can be translated into protein within a cell or in vitro. Cosuppression constructs in plants have been previously designed by focusing on overexpression of a nucleic acid sequence having homology to a native mRNA, in the sense orientation, which results in the reduction of all RNA having homology to the overexpressed sequence (see Vaucheret et al., Plant J. 16:651-659 (1998); and Gura, Nature 404:804-808 (2000)).

Another variation describes the use of plant viral sequences to direct the suppression of proximal mRNA encoding sequences (PCT Publication No. WO 98/36083 published on Aug. 20, 1998).

RNA interference refers to the process of sequence-specific post-transcriptional gene silencing in animals mediated by short interfering RNAs (siRNAs) (Fire et al., Nature 391:806 (1998)). The corresponding process in plants is commonly referred to as post-transcriptional gene silencing (PTGS) or RNA silencing and is also referred to as quelling in fungi. The process of post-transcriptional gene silencing is thought to be an evolutionarily-conserved cellular defense mechanism used to prevent the expression of foreign genes and is commonly shared by diverse flora and phyla (Fire et al., Trends Genet. 15:358 (1999)).

Small RNAs play an important role in controlling gene expression. Regulation of many developmental processes, including flowering, is controlled by small RNAs. It is now possible to engineer changes in gene expression of plant genes by using transgenic constructs which produce small RNAs in the plant.

Small RNAs appear to function by base-pairing to complementary RNA or DNA target sequences. When bound to RNA, small RNAs trigger either RNA cleavage or translational inhibition of the target sequence. When bound to DNA target sequences, it is thought that small RNAs can mediate DNA methylation of the target sequence. The consequence of these events, regardless of the specific mechanism, is that gene expression is inhibited.

MicroRNAs (miRNAs) are noncoding RNAs of about 19 to about 24 nucleotides (nt) in length that have been identified in both animals and plants (Lagos-Quintana et al., Science 294:853-858 (2001), Lagos-Quintana et al., Curr. Biol. 12:735-739 (2002); Lau et al., Science 294:858-862 (2001); Lee and Ambros, Science 294:862-864 (2001); Llave et al., Plant Cell 14:1605-1619 (2002); Mourelatos et al., Genes. Dev. 16:720-728 (2002); Park et al., Curr. Biol. 12:1484-1495 (2002); Reinhart et al., Genes. Dev. 16:1616-1626 (2002)). They are processed from longer precursor transcripts that range in size from approximately 70 to 200 nt, and these precursor transcripts have the ability to form stable hairpin structures.

MicroRNAs (miRNAs) appear to regulate target genes by binding to complementary sequences located in the transcripts produced by these genes. It seems likely that miRNAs can enter at least two pathways of target gene regulation: (1) translational inhibition; and (2) RNA cleavage. MicroRNAs entering the RNA cleavage pathway are analogous to the 21-25 nt short interfering RNAs (siRNAs) generated during RNA interference (RNAi) in animals and posttranscriptional gene silencing (PTGS) in plants, and likely are incorporated into an RNA-induced silencing complex (RISC) that is similar or identical to that seen for RNAi.

Regulatory Sequences:

A recombinant DNA construct (including a suppression DNA construct) of the present invention may comprise at least one regulatory sequence.

A regulatory sequence may be a promoter.

A number of promoters can be used in recombinant DNA constructs (and suppression DNA constructs) of the present invention. The promoters can be selected based on the desired outcome, and may include constitutive, tissue-specific, inducible, or other promoters for expression in the host organism.

Promoters that cause a gene to be expressed in most cell types at most times are commonly referred to as “constitutive promoters”.

High level, constitutive expression of the candidate gene under control of the 35S or UBI promoter may (or may not) have pleiotropic effects, although candidate gene efficacy may be estimated when driven by a constitutive promoter. Use of tissue-specific and/or stress-specific promoters may eliminate undesirable effects, but retain the ability to enhance nitrogen tolerance. This type of effect has been observed in Arabidopsis for drought and cold tolerance (Kasuga et al., Nature Biotechnol. 17:287-91 (1999)).

Suitable constitutive promoters for use in a plant host cell include, for example, the core promoter of the Rsyn7 promoter and other constitutive promoters disclosed in WO 99/43838 and U.S. Pat. No. 6,072,050; the core CaMV 35S promoter (Odell et al., Nature 313:810-812 (1985)); rice actin (McElroy et al., Plant Cell 2:163-171 (1990)); ubiquitin (Christensen et al., Plant Mol. Biol. 12:619-632 (1989) and Christensen et al., Plant Mol. Biol. 18:675-689 (1992)); pEMU (Last et al., Theor. Appl. Genet. 81:581-588 (1991)); MAS (Velten et al., EMBO J. 3:2723-2730 (1984)); ALS promoter (U.S. Pat. No. 5,659,026), and the like. Other constitutive promoters include, for example, those discussed in U.S. Pat. Nos. 5,608,149; 5,608,144; 5,604,121; 5,569,597; 5,466,785; 5,399,680; 5,268,463; 5,608,142; and 6,177,611.

In choosing a promoter to use in the methods of the invention, it may be desirable to use a tissue-specific or developmentally regulated promoter.

A tissue-specific or developmentally regulated promoter is a DNA sequence which regulates the expression of a DNA sequence selectively in the cells/tissues of a plant critical to tassel development, seed set, or both, and limits the expression of such a DNA sequence to the period of tassel development or seed maturation in the plant. Any identifiable promoter may be used in the methods of the present invention which causes the desired temporal and spatial expression.

Promoters which are seed or embryo-specific and may be useful in the invention include soybean Kunitz trypsin inhibitor (Kti3, Jofuku and Goldberg, Plant Cell 1:1079-1093 (1989)), patatin (potato tubers) (Rocha-Sosa, M., et al., EMBO J. 8:23-29 (1989)), convicilin, vicilin, and legumin (pea cotyledons) (Rerie, W. G., et al., Mol. Gen. Genet. 259:149-157 (1991); Newbigin, E. J., et al., Planta 180:461-470 (1990); Higgins, T. J. V., et al., Plant. Mol. Biol. 11:683-695 (1988)), zein (maize endosperm) (Schemthaner, J. P., et al., EMBO J. 7:1249-1255 (1988)), phaseolin (bean cotyledon) (Segupta-Gopalan, C., et al., Proc. Natl. Acad. Sci. U.S.A. 82:3320-3324 (1995)), phytohemagglutinin (bean cotyledon) (Voelker, T. et al., EMBO J. 6:3571-3577 (1987)), B-conglycinin and glycinin (soybean cotyledon) (Chen, Z-L, et al., EMBO J. 7:297-302 (1988)), glutelin (rice endosperm), hordein (barley endosperm) (Marris, C., et al., Plant Mol. Biol. 10:359-366 (1988)), glutenin and gliadin (wheat endosperm) (Colot, V., et al., EMBO J. 6:3559-3564 (1987)), and sporamin (sweet potato tuberous root) (Hattori, T., et al., Plant Mol. Biol. 14:595-604 (1990)). Promoters of seed-specific genes operably linked to heterologous coding regions in chimeric gene constructions maintain their temporal and spatial expression pattern in transgenic plants. Such examples include Arabidopsis thaliana 2S seed storage protein gene promoter to express enkephalin peptides in Arabidopsis and Brassica napus seeds (Vanderkerckhove et al., Bio/Technology 7:L929-932 (1989)), bean lectin and bean beta-phaseolin promoters to express luciferase (Riggs et al., Plant Sci. 63:47-57 (1989)), and wheat glutenin promoters to express chloramphenicol acetyl transferase (Colot et al., EMBO J. 6:3559-3564 (1987)).

Inducible promoters selectively express an operably linked DNA sequence in response to the presence of an endogenous or exogenous stimulus, for example by chemical compounds (chemical inducers) or in response to environmental, hormonal, chemical, and/or developmental signals. Inducible or regulated promoters include, for example, promoters regulated by light, heat, stress, flooding or drought, phytohormones, wounding, or chemicals such as ethanol, jasmonate, salicylic acid, or safeners.

Promoters for use in the current invention include the following: 1) the stress-inducible RD29A promoter (Kasuga et al., Nature Biotechnol. 17:287-91 (1999)); 2) the barley promoter, B22E; expression of B22E is specific to the pedicel in developing maize kernels (“Primary Structure of a Novel Barley Gene Differentially Expressed in Immature Aleurone Layers”, Klemsdal et al., Mol. Gen. Genet. 228(1/2):9-16 (1991)); and 3) maize promoter, Zag2 (“Identification and molecular characterization of ZAG1, the maize homolog of the Arabidopsis floral homeotic gene AGAMOUS”, Schmidt et al., Plant Cell 5(7):729-737 (1993); “Structural characterization, chromosomal localization and phylogenetic evaluation of two pairs of AGAMOUS-like MADS-box genes from maize”, Theissen et al., Gene 156(2):155-166 (1995); NCBI GenBank Accession No. X80206)). Zag2 transcripts can be detected five days prior to pollination to seven to eight days after pollination (“DAP”), and directs expression in the carpel of developing female inflorescences and Ciml which is specific to the nucleus of developing maize kernels. Ciml transcript is detected four to five days before pollination to six to eight DAP. Other useful promoters include any promoter which can be derived from a gene whose expression is maternally associated with developing female florets.

Additional promoters for regulating the expression of the nucleotide sequences of the present invention in plants are stalk-specific promoters. Such stalk-specific promoters include the alfalfa S2A promoter (GenBank Accession No. EF030816; Abrahams et al., Plant Mol. Biol. 27:513-528 (1995)) and S2B promoter (GenBank Accession No. EF030817) and the like, herein incorporated by reference.

Promoters may be derived in their entirety from a native gene, or be composed of different elements derived from different promoters found in nature, or even comprise synthetic DNA segments.

Promoters for use in the current invention may include: RIP2, mLIP15, ZmCOR1, Rab17, CaMV 35S, RD29A, B22E, Zag2, SAM synthetase, ubiquitin, CaMV 19S, nos, Adh, sucrose synthase, R-allele, the vascular tissue other promoters S2A (Genbank accession number EF030816) and S2B (GenBank Accession No. EF030817), and the constitutive promoter GOS2 from Zea mays. Other promoters include root promoters, such as the maize NAS2 promoter, the maize Cyclo promoter (US Publication No. 2006/0156439, published Jul. 13, 2006), the maize ROOTMET2 promoter (WO 2005/063998, published Jul. 14, 2005), the CR1BIO promoter (WO 2006/055487, published May 26, 2006), the CRWAQ81 (WO 2005/035770, published Apr. 21, 2005) and the maize ZRP2.47 promoter (NCBI Accession No. U38790; NCBI GI No. 1063664).

Recombinant DNA constructs (and suppression DNA constructs) of the present invention may also include other regulatory sequences including, but not limited to, translation leader sequences, introns, and polyadenylation recognition sequences. In another embodiment of the present invention, a recombinant DNA construct of the present invention further comprises an enhancer or silencer.

An intron sequence can be added to the 5′ untranslated region, the protein-coding region or the 3′ untranslated region to increase the amount of the mature message that accumulates in the cytosol. Inclusion of a spliceable intron in the transcription unit in both plant and animal expression constructs has been shown to increase gene expression at both the mRNA and protein levels up to 1000-fold (Buchman and Berg, Mol. Cell Biol. 8:4395-4405 (1988); Callis et al., Genes Dev. 1:1183-1200 (1987)).

Any plant can be selected for the identification of regulatory sequences and genes to be used in recombinant DNA constructs of the present invention. Examples of suitable plant targets for the isolation of genes and regulatory sequences would include but are not limited to alfalfa, apple, apricot, Arabidopsis, artichoke, arugula, asparagus, avocado, banana, barley, beans, beet, blackberry, blueberry, broccoli, brussels sprouts, cabbage, canola, cantaloupe, carrot, cassava, castorbean, cauliflower, celery, cherry, chicory, cilantro, citrus, clementines, clover, coconut, coffee, corn, cotton, cranberry, cucumber, Douglas fir, eggplant, endive, escarole, eucalyptus, fennel, figs, garlic, gourd, grape, grapefruit, honey dew, jicama, kiwifruit, lettuce, leeks, lemon, lime, Loblolly pine, linseed, maize, mango, melon, mushroom, nectarine, nut, oat, oil palm, oil seed rape, okra, olive, onion, orange, an ornamental plant, palm, papaya, parsley, parsnip, pea, peach, peanut, pear, pepper, persimmon, pine, pineapple, plantain, plum, pomegranate, poplar, potato, pumpkin, quince, radiata pine, radicchio, radish, rapeseed, raspberry, rice, rye, sorghum, Southern pine, soybean, spinach, squash, strawberry, sugarbeet, sugarcane, sunflower, sweet potato, sweetgum, tangerine, tea, tobacco, tomato, triticale, turf, turnip, a vine, watermelon, wheat, yams, and zucchini.

Compositions

A composition of the present invention is a plant comprising in its genome any of the recombinant DNA constructs (including any of the suppression DNA constructs) of the present invention (such as any of the other constructs discussed above). Compositions also include any progeny of the plant, and any seed obtained from the plant or its progeny, wherein the progeny or seed comprises within its genome the recombinant DNA construct (or suppression DNA construct). Progeny includes subsequent generations obtained by self-pollination or out-crossing of a plant. Progeny also includes hybrids and inbreds.

In hybrid seed propagated crops, mature transgenic plants can be self-pollinated to produce a homozygous inbred plant. The inbred plant produces seed containing the newly introduced recombinant DNA construct (or suppression DNA construct). These seeds can be grown to produce plants that would exhibit an altered agronomic characteristic (e.g., an increased agronomic characteristic, e.g. under nitrogen limiting conditions), or used in a breeding program to produce hybrid seed, which can be grown to produce plants that would exhibit such an altered agronomic characteristic. The seeds may be maize seeds.

The plant may be a monocotyledonous or dicotyledonous plant, for example, a maize or soybean plant, such as a maize hybrid plant or a maize inbred plant. The plant may also be sunflower, sorghum, canola, wheat, alfalfa, cotton, rice, barley, millet, sugar cane, or switchgrass.

The recombinant DNA construct may be stably integrated into the genome of the plant.

Particular embodiments include but are not limited to the following:

1. A plant (for example, a maize or soybean plant) comprising in its genome a recombinant DNA construct comprising a polynucleotide operably linked to at least one regulatory sequence, wherein said polynucleotide encodes a polypeptide having an amino acid sequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity, based on the Clustal V method of alignment, when compared to SEQ ID NO:19, 21, 23, 25, 27, 29, 30, 31, 32, 36, 38, 40, 42, 44, 46, 48, or 49, and wherein said plant exhibits increased nitrogen stress tolerance when compared to a control plant not comprising said recombinant DNA construct. The plant may further exhibit an alteration of at least one agronomic characteristic when compared to the control plant.

2. A plant (for example, a maize or soybean plant) comprising in its genome a recombinant DNA construct comprising a polynucleotide operably linked to at least one regulatory sequence, wherein said polynucleotide encodes a SNF2 domain-containing polypeptide, and wherein said plant exhibits increased nitrogen stress tolerance when compared to a control plant not comprising said recombinant DNA construct. The plant may further exhibit an alteration of at least one agronomic characteristic when compared to the control plant.

3. A plant (for example, a maize or soybean plant) comprising in its genome a recombinant DNA construct comprising a polynucleotide operably linked to at least one regulatory sequence, wherein said polynucleotide encodes a SNF2 domain-containing polypeptide, and wherein said plant exhibits an alteration of at least one agronomic characteristic under nitrogen limiting conditions when compared to a control plant not comprising said recombinant DNA construct.

4. A plant (for example, a maize or soybean plant) comprising in its genome a recombinant DNA construct comprising a polynucleotide operably linked to at least one regulatory element, wherein said polynucleotide encodes a polypeptide having an amino acid sequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity, based on the Clustal V method of alignment, when compared to SEQ ID NO:19, 21, 23, 25, 27, 29, 30, 31, 32, 36, 38, 40, 42, 44, 46, 48, or 49, and wherein said plant exhibits an alteration of at least one agronomic characteristic under nitrogen limiting conditions when compared to a control plant not comprising said recombinant DNA construct.

5. A plant (for example, a maize or soybean plant) comprising in its genome a suppression DNA construct comprising at least one regulatory element operably linked to a region derived from all or part of a sense strand or antisense strand of a target gene of interest, said region having a nucleic acid sequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity, based on the Clustal V method of alignment, when compared to said all or part of a sense strand or antisense strand from which said region is derived, and wherein said target gene of interest encodes a SNF2 domain-containing polypeptide, and wherein said plant exhibits an alteration of at least one agronomic characteristic under nitrogen limiting conditions when compared to a control plant not comprising said suppression DNA construct.

6. A plant (for example, a maize or soybean plant) comprising in its genome a suppression DNA construct comprising at least one regulatory element operably linked to all or part of: (a) a nucleic acid sequence encoding a polypeptide having an amino acid sequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity, based on the Clustal V method of alignment, when compared to SEQ ID NO:19, 21, 23, 25, 27, 29, 30, 31, 32, 36, 38, 40, 42, 44, 46, 48, or 49; or (b) a full complement of the nucleic acid sequence of (a), and wherein said plant exhibits an alteration of at least one agronomic characteristic under nitrogen limiting conditions when compared to a control plant not comprising said suppression DNA construct.

7. Any progeny of the above plants in embodiments 1-6, any seeds of the above plants in embodiments 1-6, any seeds of progeny of the above plants in embodiments 1-6, and cells from any of the above plants in embodiments 1-6 and progeny thereof.

In any of the foregoing embodiments 1-7 or any other embodiments of the present invention, the SNF2 domain-containing polypeptide may be from Arabidopsis thaliana, Zea mays, Glycine max, Glycine tabacina, Glycine soja or Glycine tomentella.

In any of the foregoing embodiments 1-7 or any other embodiments of the present invention, the recombinant DNA construct (or suppression DNA construct) may comprise at least a promoter functional in a plant as aregulatory sequence.

In any of the foregoing embodiments 1-7 or any other embodiments of the present invention, the alteration of at least one agronomic characteristic is either an increase or decrease.

In any of the foregoing embodiments 1-7 or any other embodiments of the present invention, the at least one agronomic characteristic may be selected from the group consisting of greenness, yield, growth rate, biomass, fresh weight at maturation, dry weight at maturation, fruit yield, seed yield, total plant nitrogen content, fruit nitrogen content, seed nitrogen content, nitrogen content in a vegetative tissue, whole plant amino acid content, vegetative tissue free amino acid content, fruit free amino acid content, seed free amino acid content, total plant protein content, fruit protein content, seed protein content, protein content in a vegetative tissue, drought tolerance, nitrogen uptake, resistance to root lodging, harvest index, stalk lodging, plant height, ear height, ear length, salt tolerance, early seedling vigor and seedling emergence under low temperature stress. For example, the alteration of at least one agronomic characteristic may be an increase in yield, greenness or biomass.

In any of the foregoing embodiments 1-7 or any other embodiments of the present invention, the plant may exhibit an alteration of at least one agronomic characteristic when compared, under nitrogen stress conditions, to a control plant not comprising said recombinant DNA construct (or suppression DNA construct).

One of ordinary skill in the art is familiar with protocols for simulating nitrogen conditions, whether limiting or non-limiting, and for evaluating plants that have been subjected to simulated or naturally-occurring nitrogen conditions, whether limiting or non-limiting. For example, one can simulate nitrogen conditions by giving plants less nitrogen than normally required or no nitrogen over a period of time, and one can evaluate such plants by looking for differences in agronomic characteristics, e.g., changes in physiological and/or physical condition, including (but not limited to) vigor, growth, size, or root length, or in particular, leaf color or leaf area size. Other techniques for evaluating such plants include measuring chlorophyll fluorescence, photosynthetic rates, root growth or gas exchange rates.

The Examples below describe some representative protocols and techniques for simulating nitrogen limiting conditions and/or evaluating plants under such conditions.

One can also evaluate nitrogen stress tolerance by the ability of a plant to maintain sufficient yield (for example, at least 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% yield) in field testing under simulated or naturally-occurring low or high nitrogen conditions (e.g., by measuring for substantially equivalent yield under low or high nitrogen conditions compared to normal nitrogen conditions, or by measuring for less yield loss under low or high nitrogen conditions compared to a control or reference plant).

One of ordinary skill in the art would readily recognize a suitable control or reference plant to be utilized when assessing or measuring an agronomic characteristic or phenotype of a transgenic plant in any embodiment of the present invention in which a control plant is utilized (e.g., compositions or methods as described herein). For example, by way of non-limiting illustrations:

1. Progeny of a transformed plant which is hemizygous with respect to a recombinant DNA construct (or suppression DNA construct), such that the progeny are segregating into plants either comprising or not comprising the recombinant DNA construct (or suppression DNA construct): the progeny comprising the recombinant DNA construct (or suppression DNA construct) would be typically measured relative to the progeny not comprising the recombinant DNA construct (or suppression DNA construct) (i.e., the progeny not comprising the recombinant DNA construct (or the suppression DNA construct) is the control or reference plant).

2. Introgression of a recombinant DNA construct (or suppression DNA construct) into an inbred line, such as in maize, or into a variety, such as in soybean: the introgressed line would typically be measured relative to the parent inbred or variety line (i.e., the parent inbred or variety line is the control or reference plant).

3. Two hybrid lines, where the first hybrid line is produced from two parent inbred lines, and the second hybrid line is produced from the same two parent inbred lines except that one of the parent inbred lines contains a recombinant DNA construct (or suppression DNA construct): the second hybrid line would typically be measured relative to the first hybrid line (i.e., the first hybrid line is the control or reference plant).

4. A plant comprising a recombinant DNA construct (or suppression DNA construct): the plant may be assessed or measured relative to a control plant not comprising the recombinant DNA construct (or suppression DNA construct) but otherwise having a comparable genetic background to the plant (e.g., sharing at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity of nuclear genetic material compared to the plant comprising the recombinant DNA construct (or suppression DNA construct)). There are many laboratory-based techniques available for the analysis, comparison and characterization of plant genetic backgrounds; among these are Isozyme Electrophoresis, Restriction Fragment Length Polymorphisms (RFLPs), Randomly Amplified Polymorphic DNAs (RAPDs), Arbitrarily Primed Polymerase Chain Reaction (AP-PCR), DNA Amplification Fingerprinting (DAF), Sequence Characterized Amplified Regions (SCARs), Amplified Fragment Length Polymorphisms (AFLP®s), and Simple Sequence Repeats (SSRs) which are also referred to as Microsatellites.

Furthermore, one of ordinary skill in the art would readily recognize that a suitable control or reference plant to be utilized when assessing or measuring an agronomic characteristic or phenotype of a transgenic plant would not include a plant that had been previously selected, via mutagenesis or transformation, for the desired agronomic characteristic or phenotype.

Methods

Methods include but are not limited to methods for increasing nitrogen stress tolerance in a plant, methods for evaluating nitrogen stress tolerance in a plant, methods for altering an agronomic characteristic in a plant, methods for determining an alteration of an agronomic characteristic in a plant, and methods for producing seed. The plant may be a monocotyledonous or dicotyledonous plant, for example, a maize or soybean plant. The plant may also be sunflower, sorghum, canola, wheat, alfalfa, cotton, rice, barley, millet, or sugar cane. The seed may be a maize or soybean seed, for example, a maize hybrid seed or maize inbred seed.

Methods include but are not limited to the following:

A method for transforming a cell comprising transforming a cell with any of the isolated polynucleotides of the present invention. The cell transformed by this method is also included. In particular embodiments, the cell is eukaryotic cell, e.g., a yeast, insect or plant cell, or prokaryotic, e.g., a bacterial cell.

A method for producing a transgenic plant comprising transforming a plant cell with any of the isolated polynucleotides or recombinant DNA constructs (including suppression DNA constructs) of the present invention and regenerating a transgenic plant from the transformed plant cell. The invention is also directed to the transgenic plant produced by this method, and transgenic seed obtained from this transgenic plant. The transgenic plant obtained by this method may be used in other methods of the present invention.

A method for isolating a polypeptide of the invention from a cell or culture medium of the cell, wherein the cell comprises a recombinant DNA construct comprising a polynucleotide of the invention operably linked to at least one regulatory sequence, and wherein the transformed host cell is grown under conditions that are suitable for expression of the recombinant DNA construct.

A method of altering the level of expression of a polypeptide of the invention in a host cell comprising: (a) transforming a host cell with a recombinant DNA construct of the present invention; and (b) growing the transformed host cell under conditions that are suitable for expression of the recombinant DNA construct wherein expression of the recombinant DNA construct results in production of altered levels of the polypeptide of the invention in the transformed host cell.

A method of increasing nitrogen stress tolerance in a plant, comprising: (a) introducing into a regenerable plant cell a recombinant DNA construct comprising a polynucleotide operably linked to at least one regulatory sequence (for example, a promoter functional in a plant), wherein the polynucleotide encodes a polypeptide having an amino acid sequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity, based on the Clustal V method of alignment, when compared to SEQ ID NO:19, 21, 23, 25, 27, 29, 30, 31, 32, 36, 38, 40, 42, 44, 46, 48, or 49; and (b) regenerating a transgenic plant from the regenerable plant cell after step (a), wherein the transgenic plant comprises in its genome the recombinant DNA construct and exhibits increased nitrogen stress tolerance when compared to a control plant not comprising the recombinant DNA construct. The method may further comprise (c) obtaining a progeny plant derived from the transgenic plant, wherein said progeny plant comprises in its genome the suppression DNA construct and exhibits increased nitrogen tolerance when compared to a control plant not comprising the recombinant DNA construct.

A method of increasing nitrogen stress tolerance in a plant, comprising: (a) introducing into a regenerable plant cell a suppression DNA construct comprising at least one regulatory sequence (for example, a promoter functional in a plant) operably linked to all or part of (i) a nucleic acid sequence encoding a polypeptide having an amino acid sequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity, based on the Clustal V method of alignment, when compared to SEQ ID NO:19, 21, 23, 25, 27, 29, 30, 31, 32, 36, 38, 40, 42, 44, 46, 48, or 49, or (ii) a full complement of the nucleic acid sequence of (a)(i); and (b) regenerating a transgenic plant from the regenerable plant cell after step (a), wherein the transgenic plant comprises in its genome the suppression DNA construct and exhibits increased nitrogen stress tolerance when compared to a control plant not comprising the suppression DNA construct. The method may further comprise (c) obtaining a progeny plant derived from the transgenic plant, wherein said progeny plant comprises in its genome the suppression DNA construct and exhibits increased nitrogen tolerance when compared to a control plant not comprising the suppression DNA construct.

A method of increasing nitrogen stress tolerance in a plant, comprising: (a) introducing into a regenerable plant cell a suppression DNA construct comprising at least one regulatory sequence (for example, a promoter functional in a plant) operably linked to a region derived from all or part of a sense strand or antisense strand of a target gene of interest, said region having a nucleic acid sequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity, based on the Clustal V method of alignment, when compared to said all or part of a sense strand or antisense strand from which said region is derived, and wherein said target gene of interest encodes a SNF2 domain-containing polypeptide; and (b) regenerating a transgenic plant from the regenerable plant cell after step (a), wherein the transgenic plant comprises in its genome the suppression DNA construct and exhibits increased nitrogen stress tolerance when compared to a control plant not comprising the suppression DNA construct. The method may further comprise (c) obtaining a progeny plant derived from the transgenic plant, wherein said progeny plant comprises in its genome the suppression DNA construct and exhibits increased nitrogen tolerance when compared to a control plant not comprising the suppression DNA construct.

A method of evaluating nitrogen stress tolerance in a plant, comprising (a) obtaining a transgenic plant, wherein the transgenic plant comprises in its genome a recombinant DNA construct comprising a polynucleotide operably linked to at least one regulatory sequence (for example, a promoter functional in a plant), wherein the polynucleotide encodes a polypeptide having an amino acid sequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity, based on the Clustal V method of alignment, when compared to SEQ ID NO:19, 21, 23, 25, 27, 29, 30, 31, 32, 36, 38, 40, 42, 44, 46, 48, or 49; (b) obtaining a progeny plant derived from the transgenic plant, wherein the progeny plant comprises in its genome the recombinant DNA construct; and (c) evaluating the progeny plant for nitrogen stress tolerance compared to a control plant not comprising the recombinant DNA construct.

A method of evaluating nitrogen stress tolerance in a plant, comprising (a) obtaining a transgenic plant, wherein the transgenic plant comprises in its genome a suppression DNA construct comprising at least one regulatory sequence (for example, a promoter functional in a plant) operably linked to all or part of (i) a nucleic acid sequence encoding a polypeptide having an amino acid sequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity, based on the Clustal V method of alignment, when compared to SEQ ID NO:19, 21, 23, 25, 27, 29, 30, 31, 32, 36, 38, 40, 42, 44, 46, 48, or 49; or (ii) a full complement of the nucleic acid sequence of (a)(i); (b) obtaining a progeny plant derived from the transgenic plant, wherein the progeny plant comprises in its genome the suppression DNA construct; and (c) evaluating the progeny plant for nitrogen stress tolerance compared to a control plant not comprising the suppression DNA construct.

A method of evaluating nitrogen stress tolerance in a plant, comprising (a) obtaining a transgenic plant, wherein the transgenic plant comprises in its genome a suppression DNA construct comprising at least one regulatory sequence (for example, a promoter functional in a plant) operably linked to a region derived from all or part of a sense strand or antisense strand of a target gene of interest, said region having a nucleic acid sequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity, based on the Clustal V method of alignment, when compared to said all or part of a sense strand or antisense strand from which said region is derived, and wherein said target gene of interest encodes a SNF2 domain-containing polypeptide; (b) obtaining a progeny plant derived from the transgenic plant, wherein the progeny plant comprises in its genome the suppression DNA construct; and (c) evaluating the progeny plant for nitrogen stress tolerance compared to a control plant not comprising the suppression DNA construct.

A method of determining an alteration of an agronomic characteristic in a plant, comprising (a) obtaining a transgenic plant, wherein the transgenic plant comprises in its genome a recombinant DNA construct comprising a polynucleotide operably linked to at least on regulatory sequence (for example, a promoter functional in a plant), wherein said polynucleotide encodes a polypeptide having an amino acid sequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, %, 97%, 98%, 99%, or 100% 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96 sequence identity, based on the Clustal V method of alignment, when compared to SEQ ID NO:19, 21, 23, 25, 27, 29, 30, 31, 32, 36, 38, 40, 42, 44, 46, 48, or 49; (b) obtaining a progeny plant derived from the transgenic plant, wherein the progeny plant comprises in its genome the recombinant DNA construct; and (c) determining whether the progeny plant exhibits an alteration of at least one agronomic characteristic when compared, optionally under nitrogen limiting conditions, to a control plant not comprising the recombinant DNA construct.

A method of determining an alteration of an agronomic characteristic in a plant, comprising (a) obtaining a transgenic plant, wherein the transgenic plant comprises in its genome a suppression DNA construct comprising at least one regulatory sequence (for example, a promoter functional in a plant) operably linked to all or part of (i) a nucleic acid sequence encoding a polypeptide having an amino acid sequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity, based on the Clustal V method of alignment, when compared to SEQ ID NO:19, 21, 23, 25, 27, 29, 30, 31, 32, 36, 38, 40, 42, 44, 46, 48, or 49; or (ii) a full complement of the nucleic acid sequence of (i); (b) obtaining a progeny plant derived from the transgenic plant, wherein the progeny plant comprises in its genome the suppression DNA construct; and (c) determining whether the progeny plant exhibits an alteration of at least one agronomic characteristic when compared, optionally under nitrogen limiting conditions, to a control plant not comprising the suppression DNA construct.

A method of determining an alteration of an agronomic characteristic in a plant, comprising (a) obtaining a transgenic plant, wherein the transgenic plant comprises in its genome a suppression DNA construct comprising at least one regulatory sequence (for example, a promoter functional in a plant) operably linked to a region derived from all or part of a sense strand or antisense strand of a target gene of interest, said region having a nucleic acid sequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity, based on the Clustal V method of alignment, when compared to said all or part of a sense strand or antisense strand from which said region is derived, and wherein said target gene of interest encodes a SNF2 domain-containing polypeptide; (b) obtaining a progeny plant derived from the transgenic plant, wherein the progeny plant comprises in its genome the suppression DNA construct; and (c) determining whether the progeny plant exhibits an alteration of at least one agronomic characteristic when compared, optionally under nitrogen limiting conditions, to a control plant not comprising the suppression DNA construct.

A method of producing seed (for example, seed that can be sold as a nitrogen stress tolerant product offering) comprising any of the preceding methods, and further comprising obtaining seeds from said progeny plant, wherein said seeds comprise in their genome said recombinant DNA construct (or suppression DNA construct).

In any of the preceding methods or any other embodiments of methods of the present invention, in said introducing step said regenerable plant cell may comprises a callus cell, an embryogenic callus cell, a gametic cell, a meristematic cell, or a cell of an immature embryo. The regenerable plant cells may derive from an inbred maize plant.

In any of the preceding methods or any other embodiments of methods of the present invention, said regenerating step may comprise: (i) culturing said transformed plant cells in a media comprising an embryogenic promoting hormone until callus organization is observed; (ii) transferring said transformed plant cells of step (i) to a first media which includes a tissue organization promoting hormone; and (iii) subculturing said transformed plant cells after step (ii) onto a second media, to allow for shoot elongation, root development or both.

In any of the preceding methods or any other embodiments of methods of the present invention, the at least one agronomic characteristic may be selected from the group consisting of greenness, yield, growth rate, biomass, fresh weight at maturation, dry weight at maturation, fruit yield, seed yield, total plant nitrogen content, fruit nitrogen content, seed nitrogen content, nitrogen content in a vegetative tissue, whole plant amino acid content, vegetative tissue free amino acid content, fruit free amino acid content, seed free amino acid content, total plant protein content, fruit protein content, seed protein content, protein content in a vegetative tissue, drought tolerance, nitrogen uptake, resistance to root lodging, harvest index, stalk lodging, plant height, ear height, ear length, salt tolerance, early seedling vigor and seedling emergence under low temperature stress. The alteration of at least one agronomic characteristic may be an increase in yield, greenness or biomass.

In any of the preceding methods or any embodiments of methods of the present invention, the plant may exhibit the alteration of at least one agronomic characteristic when compared, under nitrogen stress conditions, to a control plant not comprising said recombinant DNA construct (or suppression DNA construct).

In any of the preceding methods or any other embodiments of methods of the present invention, alternatives exist for introducing into a regenerable plant cell a recombinant DNA construct comprising a polynucleotide operably linked to at least one regulatory sequence. For example, one may introduce into a regenerable plant cell a regulatory sequence (such as one or more enhancers, for example, as part of a transposable element), and then screen for an event in which the regulatory sequence is operably linked to an endogenous gene encoding a polypeptide of the instant invention.

The introduction of recombinant DNA constructs of the present invention into plants may be carried out by any suitable technique, including but not limited to direct DNA uptake, chemical treatment, electroporation, microinjection, cell fusion, infection, vector mediated DNA transfer, bombardment, or Agrobacterium mediated transformation. Techniques for plant transformation and regeneration have been described in International Patent Publication WO 2009/006276, the contents of which are herein incorporated by reference.

The development or regeneration of plants containing the foreign, exogenous isolated nucleic acid fragment that encodes a protein of interest is well known in the art. The regenerated plants may be self-pollinated to provide homozygous transgenic plants. Otherwise, pollen obtained from the regenerated plants is crossed to seed-grown plants of agronomically important lines. Conversely, pollen from plants of these important lines is used to pollinate regenerated plants. A transgenic plant of the present invention containing a desired polypeptide is cultivated using methods well known to one skilled in the art.

EXAMPLES

The present invention is further illustrated in the following Examples, in which parts and percentages are by weight and degrees are Celsius, unless otherwise stated. It should be understood that these Examples, while indicating embodiments of the invention, are given by way of illustration only. From the above discussion and these Examples, one skilled in the art can ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. Furthermore, various modifications of the invention in addition to those shown and described herein will be apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the appended claims.

Example 1 Creation of an Arabidopsis Population with Activation-Tagged Genes

An 18.49-kb T-DNA based binary construct was created, pHSbarENDs2 (SEQ ID NO:1; FIG. 1), that contains four multimerized enhancer elements derived from the Cauliflower Mosaic Virus 35S promoter (corresponding to sequences −341 to −64, as defined by Odell et al., Nature 313:810-812 (1985)). The construct also contains vector sequences (pUC9) and a poly-linker (SEQ ID NO:11) to allow plasmid rescue, transposon sequences (Ds) to remobilize the T-DNA, and the bar gene to allow for glufosinate selection of transgenic plants. In principle, only the 10.8-kb segment from the right border (RB) to left border (LB) inclusive will be transferred into the host plant genome. Since the enhancer elements are located near the RB, they can induce cis-activation of genomic loci following T-DNA integration.

Arabidopsis activation-tagged populations were created by whole plant Agrobacterium transformation. The pHSbarENDs2 construct was transformed into Agrobacterium tumefaciens strain C58, grown in lysogeny broth medium at 25° C. to OD600˜1.0. Cells were then pelleted by centrifugation and resuspended in an equal volume of 5% sucrose/0.05% Silwet L-77 (OSI Specialties, Inc). At early bolting, soil grown Arabidopsis thaliana ecotype Col-0 were top watered with the Agrobacterium suspension. A week later, the same plants were top watered again with the same Agrobacterium strain in sucrose/Silwet. The plants were then allowed to set seed as normal. The resulting T1 seed were sown on soil, and transgenic seedlings were selected by spraying with glufosinate (FINALE®; AgrEvo; Bayer Environmental Science). A total of 100,000 glufosinate resistant T1 seedlings were selected. T2 seed from each line was kept separate.

Example 2 Screens to Identify Lines with Tolerance to Low Nitrogen

From each of 100,000 separate T1 activation-tagged lines, eleven T2 plants are sown on square plates (15 mm×15 mm) containing 0.5× N-Free Hoagland's, 0.4 mM potassium nitrate, 0.1% sucrose, 1 mM MES and 0.25% Phytagel™ (Low N medium). Five lines are plated per plate, and the inclusion of 9 wild-type individuals on each plate makes for a total of 64 individuals in an 8×8 grid pattern (see FIG. 12). Plates are kept for three days in the dark at 4° C. to stratify seeds, and then placed horizontally for nine days at 22° C. light and 20° C. dark. Photoperiod is sixteen hours light and eight hours dark, with an average light intensity of ˜200 mmol/m²/s. Plates are rotated and shuffled daily within each shelf. At day twelve (nine days of growth), seedling status is evaluated by imaging the entire plate.

After masking the plate image to remove background color, two different measurements are collected for each individual: total rosette area, and the percentage of color that falls into a green color bin. Using hue, saturation and intensity data (HSI), the green color bin consists of hues 50 to 66. Total rosette area is used as a measure of plant biomass, whereas the green color bin was shown by dose-response studies to be an indicator of nitrogen assimilation (see FIG. 13).

Lines with a significant increase in total rosette area and/or green color bin, when compared to the wild-type controls, are designated as Phase 1 hits. Phase 1 hits are re-screened in duplicate under the same assay conditions (Phase 2 screen). A Phase 3 screen is also employed to further validate mutants that passed through Phases 1 and 2. In Phase 3, each line is plated separately on Low N medium, such that 32 T2 individuals are grown next to 32 wild-type individuals on one plate, providing greater statistical rigor to the analysis. If a line shows a significant difference from the controls in Phase 3, the line is then considered a validated nitrogen-deficiency tolerant line.

Example 3 Identification of Activation-Tagged Genes

Genes flanking the T-DNA insert in nitrogen tolerant lines are identified using one, or both, of the following two standard procedures: (1) thermal asymmetric interlaced (TAIL) PCR (Liu et al., Plant J. 8:457-63 (1995)); and (2) SAIFF PCR (Siebert et al., Nucleic Acids Res. 23:1087-1088 (1995)). In lines with complex multimerized T-DNA inserts, TAIL PCR and SAIFF PCR may both prove insufficient to identify candidate genes. In these cases, other procedures, including inverse PCR, plasmid rescue and/or genomic library construction, can be employed.

A successful result is one where a single TAIL or SAIFF PCR fragment contains a T-DNA border sequence and Arabidopsis genomic sequence. Once a tag of genomic sequence flanking a T-DNA insert is obtained, candidate genes are identified by alignment to publicly available Arabidopsis genome sequence. Specifically, the annotated gene nearest the 35S enhancer elements/T-DNA RB are candidates for genes that are activated.

To verify that an identified gene is truly near a T-DNA and to rule out the possibility that the TAIL/SAIFF fragment is a chimeric cloning artifact, a diagnostic PCR on genomic DNA is done with one oligo in the T-DNA and one oligo specific for the candidate gene. Genomic DNA samples that give a PCR product are interpreted as representing a T-DNA insertion. This analysis also verifies a situation in which more than one insertion event occurs in the same line, e.g., if multiple differing genomic fragments are identified in TAIL and/or SAIFF PCR analyses.

Example 4 Identification of Activation-Tagged Gene that Encodes a SNF2 Domain-Containing Polypeptide

An activation tagged-line (line 112579) showing nitrogen-deficiency tolerance was further analyzed. DNA from the line was extracted, and genes flanking the T-DNA insert in the mutant line were identified using ligation-mediated PCR (Siebert et al., Nucleic Acids Res. 23:1087-1088 (1995)). A single amplified fragment was identified that contained a T-DNA border sequence and Arabidopsis genomic sequence. Once a tag of genomic sequence flanking a T-DNA insert was obtained, a candidate gene was identified by alignment to the completed Arabidopsis genome. Specifically, the annotated gene nearest the 35S enhancer elements/T-DNA RB was the candidate for the gene activated in the line. In the case of line 112579 the gene nearest the 35S enhancers was At1g61140, encoding the Arabidopsis thaliana SNF2 domain-containing polypeptide.

Example 5 Validation of Candidate Arabidopsis Gene (At1g61140) via Transformation into Arabidopsis

Candidate genes can be transformed into Arabidopsis and overexpressed under the 35S promoter. If the same or similar phenotype is observed in the transgenic line as in the parent activation-tagged line, then the candidate gene is considered to be a validated “lead gene” in Arabidopsis.

The candidate Arabidopsis gene (At1g61140), encoding a SNF2 domain-containing polypeptide, was tested for its ability to confer nitrogen-deficiency tolerance in the following manner. Primers were designed to amplify variant At1g61140.1.

The At1g61140.1 cDNA (SEQ ID NO:24) was amplified by RT-PCR with the following primers:

1. At1g61140-5′ attB forward primer (SEQ ID NO:33)

The forward primer contains the attB1 sequence (ACAAGTTTGTACAAAAAAGCAGGCT; SEQ ID NO:12) and a consensus Kozak sequence (CAACA) upstream of the first 21 nucleotides of the protein-coding region, beginning with the ATG start codon, of said cDNA.

2. At1g61140-3′ attB reverse primer (SEQ ID NO:34)

The reverse primer contains the attB2 sequence (ACCACTTTGTACAAGAAAGCTGGGT; SEQ ID NO:13) adjacent to the reverse complement of the last 21 nucleotides of the protein-coding region, beginning with the reverse complement of the stop codon, of said cDNA.

Using the INVITROGEN™ GATEWAY® CLONASE™ technology, a BP Recombination Reaction was performed for the RT-PCR product with pDONR™Zeo (SEQ ID NO:2; FIG. 2). This process removes the bacteria lethal ccdB gene, as well as the chloramphenicol resistance gene (CAM), from pDONR™Zeo and directionally clones the PCR product with flanking attB1 and attB2 sites, creating an entry clone. A positively identified entry clone was used for a subsequent LR Recombination Reaction with a destination vector, as follows.

A 16.8-kb T-DNA based binary vector (destination vector), called pBC-yellow (SEQ ID NO:4; FIG. 4), was constructed with a 1.3-kb 35S promoter immediately upstream of the INVITROGEN™ GATEWAY C1 conversion insert, which contains the bacterial lethal ccdB gene as well as the chloramphenicol resistance gene (CAM) flanked by attR1 and attR2 sequences. The vector also contains the RD29a promoter driving expression of the gene for ZS-Yellow (INVITROGEN™), which confers yellow fluorescence to transformed seed. Using the INVITROGEN™ GATEWAY® technology, an LR Recombination Reaction was performed with the entry clone containing the nucleotide coding sequence of At1g61140.1 (SEQ ID NO:24) and the pBC-yellow vector; however, either of the other variants could also be used (SEQ ID NOs:26 and 28). This amplification allowed for rapid and directional cloning of At1g61140.1 (SNF2.1; SEQ ID NO:24) behind the 35S promoter in pBC-yellow.

Applicants then introduced the 35S promoter:At1g61140 expression constructs into wild-type Arabidopsis ecotype Col-0, using the same Agrobacterium-mediated transformation procedure described in Example 1. Transgenic T1 seeds were selected by yellow fluorescence, and 32 of these T1 seeds were plated next to 32 wild-type Arabidopsis ecotype Col-0 seeds on low nitrogen medium. All subsequent growth and imaging conditions were performed as described in Example 1. It was found that the original phenotype from activation tagging, tolerance to nitrogen limiting conditions, could be recapitulated in wild-type Arabidopsis plants that were transformed with a construct where an At1g61140 gene was directly expressed by the 35S promoter.

Example 6A Preparation of cDNA Libraries and Isolation and Sequencing of cDNA Clones

cDNA libraries may be prepared by any one of many methods available. For example, the cDNAs may be introduced into plasmid vectors by first preparing the cDNA libraries in UNI-ZAP™ XR vectors according to the manufacturer's protocol (Stratagene Cloning Systems, La Jolla, Calif.). The UNI-ZAP™ XR libraries are converted into plasmid libraries according to the protocol provided by Stratagene. Upon conversion, cDNA inserts will be contained in the plasmid vector pBLUESCRIPT®. In addition, the cDNAs may be introduced directly into precut BLUESCRIPT® II SK(+) vectors (Stratagene) using T4 DNA ligase (New England Biolabs), followed by transfection into DH10B cells according to the manufacturer's protocol (GIBCO BRL Products). Once the cDNA inserts are in plasmid vectors, plasmid DNAs are prepared from randomly picked bacterial colonies containing recombinant pBLUESCRIPT® plasmids, or the insert cDNA sequences are amplified via polymerase chain reaction using primers specific for vector sequences flanking the inserted cDNA sequences. Amplified insert DNAs or plasmid DNAs are sequenced in dye-primer sequencing reactions to generate partial cDNA sequences (expressed sequence tags or “ESTs”; see Adams et al., Science 252:1651-1656 (1991)). The resulting ESTs are analyzed using a Perkin Elmer Model 377 fluorescent sequencer.

Full-insert sequence (FIS) data is generated utilizing a modified transposition protocol. Clones identified for FIS are recovered from archived glycerol stocks as single colonies, and plasmid DNAs are isolated via alkaline lysis. Isolated DNA templates are reacted with vector primed M13 forward and reverse oligonucleotides in a PCR-based sequencing reaction and loaded onto automated sequencers. Confirmation of clone identification is performed by sequence alignment to the original EST sequence from which the FIS request is made.

Confirmed templates are transposed via the Primer Island transposition kit (PE Applied Biosystems, Foster City, Calif.) which is based upon the Saccharomyces cerevisiae Ty1 transposable element (Devine and Boeke, Nucleic Acids Res. 22:3765-3772 (1994)). The in vitro transposition system places unique binding sites randomly throughout a population of large DNA molecules. The transposed DNA is then used to transform DH10B electro-competent cells (GIBCO BRL/Life Technologies, Rockville, Md.) via electroporation. The transposable element contains an additional selectable marker (named DHFR; Fling and Richards, Nucleic Acids Res. 11:5147-5158 (1983)), allowing for dual selection on agar plates of only those subclones containing the integrated transposon. Multiple subclones are randomly selected from each transposition reaction, plasmid DNAs are prepared via alkaline lysis, and templates are sequenced (ABI PRISM dye-terminator ReadyReaction mix) outward from the transposition event site, utilizing unique primers specific to the binding sites within the transposon.

Sequence data is collected (ABI PRISM® Collections) and assembled using Phred and Phrap (Ewing et al., Genome Res. 8:175-185 (1998); Ewing et al., Genome Res. 8:186-194 (1998)). Phred is a public domain software program which re-reads the ABI sequence data, re-calls the bases, assigns quality values, and writes the base calls and quality values into editable output files. The Phrap sequence assembly program uses these quality values to increase the accuracy of the assembled sequence contigs. Assemblies are viewed by the Consed sequence editor (Gordon et al., Genome Res. 8:195-202 (1998)).

In some of the clones the cDNA fragment corresponds to a portion of the 3′-terminus of the gene and does not cover the entire open reading frame. In order to obtain the upstream information one of two different protocols is used. The first of these methods results in the production of a fragment of DNA containing a portion of the desired gene sequence while the second method results in the production of a fragment containing the entire open reading frame. Both of these methods use two rounds of PCR amplification to obtain fragments from one or more libraries. The libraries sometimes are chosen based on previous knowledge that the specific gene should be found in a certain tissue and sometimes are randomly-chosen. Reactions to obtain the same gene may be performed on several libraries in parallel or on a pool of libraries. Library pools are normally prepared using from 3 to 5 different libraries and normalized to a uniform dilution. In the first round of amplification both methods use a vector-specific (forward) primer corresponding to a portion of the vector located at the 5′-terminus of the clone coupled with a gene-specific (reverse) primer. The first method uses a sequence that is complementary to a portion of the already known gene sequence while the second method uses a gene-specific primer complementary to a portion of the 3′-untranslated region (also referred to as UTR). In the second round of amplification a nested set of primers is used for both methods. The resulting DNA fragment is ligated into a pBLUESCRIPT® vector using a commercial kit and following the manufacturer's protocol. This kit is selected from many available from several vendors including INVITROGEN™ (Carlsbad, Calif.), Promega Biotech (Madison, Wis.), and GIBCO-BRL (Gaithersburg, Md.). The plasmid DNA is isolated by alkaline lysis method and submitted for sequencing and assembly using Phred/Phrap, as above.

Example 6B Preparation of cDNA Libraries and Obtainment of Sequences

mRNAs can be isolated using the Qiagen RNA isolation kit for total RNA isolation, followed by mRNA isolation via attachment to oligo(dT) Dynabeads from Invitrogen (Life Technologies, Carlsbad, Calif.), and sequencing libraries can be prepared using the standard mRNA-Seq kit and protocol from Illumina, Inc. (San Diego, Calif.). In this method, mRNAs are fragmented using a ZnCl₂ solution, reverse transcribed into cDNA using random primers, end repaired to create blunt end fragments, 3′ A-tailed, and ligated with Illumina paired-end library adaptors. Ligated cDNA fragments can then be PCR amplified using Illumina paired-end library primers, and purified PCR products can be checked for quality and quantity on the Agilent Bioanalyzer DNA 1000 chip prior to sequencing on the Genome Analyzer II equipped with a paired end module.

Reads from the sequencing runs can be soft-trimmed prior to assembly such that the first base pair of each read with an observed FASTQ quality score lower than 15 and all subsequent bases are clipped using a Python script. The Velvet assembler (Zerbino et al. Genome Research 18:821-9 (2008)) can be run under varying kmer and coverage cutoff parameters to produce several putative assemblies along a range of stringency. The contiguous sequences (contigs) within those assemblies can be combined into clusters using Vmatch software (available on the Vmatch website) such that contigs which are identified as substrings of longer contigs are grouped and eliminated, leaving a non-redundant set of longest “sentinel” contigs. These non-redundant sets can be used in alignments to homologous sequences from known model plant species.

If a contig does not represent a complete gene the non-redundant sets can be re-queried via Blast or a Perl Script with the sequences discovered in the first search. If sequences that extend the ends of the contigs are discovered, they can be assembled with the original sequences with a desktop assembler such as DNAStar's SeqMan, or GeneCode's Sequencher. These steps can be repeated until no further extending sequences are found. For transcripts that still are not complete, gene fragments that theoretically belong together (based on homology to other grasses) can be artificially joined with linking sequence from another grass.

Example 7 Identification of cDNA Sequences

cDNA sequences encoding SNF2 domain-containing polypeptides are identified by conducting BLAST (Basic Local Alignment Search Tool; Altschul et al., J. Mol. Biol. 215:403-410 (1993); see also the explanation of the BLAST algorithm on the world wide web site for the National Center for Biotechnology Information at the National Library of Medicine of the National Institutes of Health) searches for similarity to amino acid sequences contained in the BLAST “nr” database (comprising all non-redundant GenBank CDS translations, sequences derived from the 3-dimensional structure Brookhaven Protein Data Bank, the last major release of the SWISS-PROT protein sequence database, EMBL, and DDBJ databases). The DNA sequences can be translated in all reading frames and compared for similarity to all publicly available protein sequences contained in the “nr” database using the BLASTX algorithm (Gish and States, Nat. Genet. 3:266-272 (1993)) provided by the NCBI. The polypeptides encoded by the cDNA sequences can be analyzed for similarity to all publicly available amino acid sequences contained in the “nr” database using the BLASTP algorithm provided by the National Center for Biotechnology Information (NCBI). For convenience, the P-value (probability) or the E-value (expectation) of observing a match of a cDNA-encoded sequence to a sequence contained in the searched databases merely by chance as calculated by BLAST are reported herein as “pLog” values, which represent the negative of the logarithm of the reported P-value or E-value. Accordingly, the greater the pLog value, the greater the likelihood that the cDNA-encoded sequence and the BLAST “hit” represent homologous proteins.

EST sequences can be compared to the GenBank database as described above. ESTs that contain sequences more 5- or 3-prime can be found by using the BLASTN algorithm (Altschul et al., Nucleic Acids Res. 25:3389-3402 (1997)) against the Dupont proprietary database comparing nucleotide sequences that share common or overlapping regions of sequence homology. Where common or overlapping sequences exist between two or more nucleic acid fragments, the sequences can be assembled into a single contiguous nucleotide sequence, thus extending the original fragment in either the 5 or 3 prime direction. Once the most 5-prime EST is identified, its complete sequence can be determined by Full Insert Sequencing.

Homologous genes belonging to different species can be found by comparing the amino acid sequence of a known gene (from either a proprietary source or a public database) against an EST database using the tBLASTn algorithm. The tBLASTn algorithm searches an amino acid query against a nucleotide database that is translated in all 6 reading frames. This search allows for differences in nucleotide codon usage between different species, and for codon degeneracy.

Example 8A Characterization of cDNA Sequences Encoding SNF2 Domain-Containing Polypeptides

cDNA libraries representing mRNAs from various tissues of Zea mays (maize), Eragrostis nindensis (Resurrection grass), and Paspalum notatum (Bahiagrass) were prepared. The characteristics of the libraries are described below.

TABLE 2 cDNA Libraries from Maize Amino Library Description (tissue) Clone Nucleotide acid cfp1n Maize Tassel V7 to cfp1n.pk008.f7:fis SEQ ID SEQ ID V12 pooled, Full- NO: 18 NO: 19 length enriched normalized cfp4n Maize Pollinated ear, cfp4n.pk061.o18:fis SEQ ID SEQ ID pooled 48_72 hrs NO: 20 NO: 21 postpollination, Full-length enriched normalized p0016 Tassel shoots, p0016.ctsca12r SEQ ID SEQ ID pooled, 0.1-1.4 cm NO: 22 NO: 23 N/A Vegetative stage N/A SEQ ID SEQ ID roots from NO: 35 NO: 36 Resurrection grass (Eragrostis nindensis) N/A Vegetative stage N/A SEQ ID SEQ ID roots from NO: 37 NO: 38 Bahiagrass (Paspalum notatum)

As shown in Table 3, FIGS. 16A-AM, and FIG. 17, cDNAs identified in Table 2 encode polypeptides similar to the SNF2 domain-containing polypeptides from Arabidopsis thaliana (At1g61140.1 (GI No. 186492170;SEQ ID NO:25); At1g61140.2 (GI No. 186492172;SEQ ID NO:27); and At1g61140.3 (GI No. 186492175;SEQ ID NO:29)) and to the SNF2 domain-containing polypeptides from Oryza sativa (GI No. 53792213 corresponding to SEQ ID NO:30, GI No. 218200575 corresponding to SEQ ID NO:31, and GI No. 90399293 corresponding to SEQ ID NO:32) and from Sorghum bicolor (GI No. 242058897 corresponding to SEQ ID NO:49).

Shown in Table 3 (non-patent literature) and Table 4 (patent literature) are the BLASTP results for individual ESTs (“EST”), the sequences of the entire cDNA inserts comprising the indicated cDNA clones (“FIS”), the sequences of contigs assembled from two or more EST, FIS or PCR sequences (“Contig”), or sequences encoding an entire or functional protein derived from an FIS or a contig (“CGS”). Also shown in Tables 3 and 4 are the percent sequence identity values for each pair of amino acid sequences using the Clustal V method of alignment with default parameters (described below).

TABLE 3 BLASTP Results for Polypeptides Homologous to SNF2 Domain-Containing Polypeptides BLAST Sequence % pLog (SEQ ID NO: #) Status NCBI GI No. identity Score cfp1n.pk008.f7:fis CGS 53792213 100.0 98 (SEQ ID NO: 19) (SEQ ID NO: 30) cfp4n.pk061.o18:fis CGS 218200575 100.0 >250 (SEQ ID NO: 21) (SEQ ID NO: 31) contig of: CGS 90399293 100.0 >250 p0016.ctsca12r (SEQ ID NO: 32) (SEQ ID NO: 23) SEQ ID NO: 36 CGS 242058897 81.7 >250 (SEQ ID NO: 49) SEQ ID NO: 38 CGS 242058897 85.0 >250 (SEQ ID NO: 49)

TABLE 4 BLASTP Results for Polypeptides Homologous to SNF2 Domain-Containing Polypeptides BLAST Sequence % pLog (SEQ ID NO: #) Status Reference Identity score cfp1n.pk008.f7:fis CGS SEQ ID NO: 17848 51.83 109 (SEQ ID NO: 19) In US20080229439 SEQ ID NO: 25068 In US20080229439 SEQ ID NO: 17848 In US20070192889 SEQ ID NO: 25068 In US20070192889 SEQ ID NO: 110654 In US20040123343 cfp4n.pk061.o18:fis CGS SEQ ID NO: 48529 72.51 >250 (SEQ ID NO: 21) In US20060123505 contig of: CGS SEQ ID NO: 55175 60.02 >250 p0016.ctsca12r In US20060123505 (SEQ ID NO: 23) SEQ ID NO: 36 CGS SEQ ID NO: 16967 79.4 >250 In US20090094717 SEQ ID NO: 38 CGS SEQ ID NO: 16967 83.9 >250 In US20090094717

Example 8B Identification of Other SNF2 Domain-Containing Polypeptides

Sequences homologous to the lead genes that encode SNF2 domain-containing proteins can be identified using sequence comparison algorithms such as BLAST (Basic Local Alignment Search Tool; Altschul et al., J. Mol. Biol. 215:403-410 (1993); see also the explanation of the BLAST algorithm on the world wide web site for the National Center for Biotechnology Information at the National Library of Medicine of the National Institutes of Health). For instance, the amino acid sequence of the protein encoded by At1g61140 was used as a query against the public database using BlastP, and the polypeptide sequences represented in SEQ ID NOs:40, 42, and 48 were subsequently identified as homologs (corresponding nucleotides sequences are SEQ ID NO:39, 41, and 47, respectively). Also, a TblastN search against public BAC sequences identified the maize homolog represented by SEQ ID NO:44 (corresponding nucleotide sequence is SEQ ID NO:43).

Example 8C Sequence Alignment and Percent Identity Calculations for SNF2 Domain-Containing Polypeptides

FIGS. 16A-AM present an alignment of the amino acid sequences set forth in SEQ ID NOs:19, 21, 23, 25, 27, 29, 30, 31, 32, 36, 38, 40, 42, 44, 46, 48, and 49. FIG. 17 is a chart of the percent sequence identity and the divergence values for each pair of amino acid sequences presented in FIGS. 16A-AM.

Sequence alignments and percent identity calculations were performed using the MEGALIGN® program of the LASERGENE® bioinformatics computing suite (DNASTAR® Inc., Madison, Wis.). Multiple alignment of the sequences was performed using the Clustal method of alignment (Higgins and Sharp (1989) CABIOS. 5:151-153) with the default parameters (GAP PENALTY=10, GAP LENGTH PENALTY=10). Default parameters for pairwise alignments using the Clustal method were KTUPLE 1, GAP PENALTY=3, WINDOW=5 and DIAGONALS SAVED=5.

Example 9 Preparation of a Plant Expression Vector Containing a Homolog to the Arabidopsis Lead Gene

Sequences homologous to the lead genes that encode SNF2 domain-containing proteins can be identified using sequence comparison algorithms such as BLAST (Basic Local Alignment Search Tool; Altschul et al., J. Mol. Biol. 215:403-410 (1993); see also the explanation of the BLAST algorithm on the world wide web site for the National Center for Biotechnology Information at the National Library of Medicine of the National Institutes of Health). The nucleotide sequences of similar genes that encode SNF2 domain-containing proteins, such as the ones described in Examples 8A-C, can be PCR-amplified by any of the following methods.

Method 1 (RNA-based): If the 5′ and 3′ sequence information for the protein-coding region is available, gene-specific primers can be designed as outlined in Example 5. RT-PCR can be used with plant RNA to obtain a nucleic acid fragment containing the protein-coding region flanked by attB1 (SEQ ID NO:12) and attB2 (SEQ ID NO:13) sequences. The primer may contain a consensus Kozak sequence (CAACA) upstream of the start codon.

Method 2 (DNA-based): Alternatively, if a cDNA clone is available, the entire cDNA insert (containing 5′ and 3′ non-coding regions) can be PCR amplified. Forward and reverse primers can be designed that contain either the attB1 sequence and vector-specific sequence that precedes the cDNA insert or the attB2 sequence and vector-specific sequence that follows the cDNA insert, respectively. For a cDNA insert cloned into the vector pBLUESCRIPT SK+, the forward primer VC062 (SEQ ID NO:16) and the reverse primer VC063 (SEQ ID NO:17) can be used.

Method 3 (genomic DNA): Genomic sequences can be obtained using long range genomic PCR capture. Primers can be designed based on the sequence of the genomic locus and the resulting PCR product can be sequenced. The sequence can be analyzed using the FGENESH (Salamov, A. and Solovyev, V. (2000) Genome Res., 10:516-522) program, and optionally, can be aligned with homologous sequences from other species to assist in identification of putative introns and exons.

Methods 1, 2, and 3 can be modified according to procedures known by one skilled in the art. For example, the primers of Method 1 may contain restriction sites instead of attB1 and attB2 sites, for subsequent cloning of the PCR product into a vector containing attB1 and attB2 sites. Additionally, Method 2 can involve amplification from a cDNA clone, a lambda clone, a BAC clone or genomic DNA.

A PCR product obtained by either method above can be combined with the GATEWAY® donor vector, such as pDONR™Zeo (SEQ ID NO:2; FIG. 2) or pDONR™221 (SEQ ID NO:3; FIG. 3), using a BP Recombination Reaction. This process removes the bacteria lethal ccdB gene, as well as the chloramphenicol resistance gene (CAM) from pDONR™Zeo or pDONR™221 and directionally clones the PCR product with flanking attB1 and attB2 sites to create an entry clone. Using the INVITROGEN™ GATEWAY® CLONASE™ technology, the sequence encoding the homologous SNF2 domain-containing polypeptide from the entry clone can then be transferred to a suitable destination vector, such as pBC-Yellow (SEQ ID NO:4; FIG. 4), PHP27840 (SEQ ID NO:5; FIG. 5), or PHP23236 (SEQ ID NO:6; FIG. 6), to obtain a plant expression vector for use with Arabidopsis, soybean, and corn, respectively.

The attP1 and attP2 sites of donor vectors pDONR™/Zeo or pDONR™221 are shown in FIGS. 2 and 3, respectively. The attR1 and attR2 sites of destination vectors pBC-Yellow, PHP27840, and PHP23236 are shown in FIGS. 4, 5 and 6, respectively.

Alternatively a MultiSite GATEWAY® LR recombination reaction between multiple entry clones and a suitable destination vector can be performed to create an expression vector.

Example 10 Preparation of Soybean Expression Vectors and Transformation of Soybean with Validated Arabidopsis Lead Genes

Soybean plants can be transformed to overexpress each validated Arabidopsis gene or the corresponding homologs from various species in order to examine the resulting phenotype.

The same GATEWAY® entry clone described in Example 5 can be used to directionally clone each gene into the PHP27840 vector (SEQ ID NO:5; FIG. 5) such that expression of the gene is under control of the SCP1 promoter.

Soybean embryos may then be transformed with the expression vector comprising sequences encoding the instant polypeptides. Techniques for soybean transformation and regeneration have been described in International Patent Publication WO 2009/006276, the contents of which are herein incorporated by reference.

T1 plants can be grown under nitrogen limiting conditions, for example, 1 mM nitrate, and analyzed for phenotypic changes. The following parameters can be quantified using image analysis: plant area, volume, growth rate and color analysis can be collected and quantified. Overexpression constructs that result in an alteration, compared to suitable control plants, in greenness (green color bin), yield, growth rate, biomass, fresh or dry weight at maturation, fruit or seed yield, total plant nitrogen content, fruit or seed nitrogen content, nitrogen content in vegetative tissue, free amino acid content in the whole plant, free amino acid content in vegetative tissue, free amino acid content in the fruit or seed, protein content in the fruit or seed, or protein content in a vegetative tissue can be considered evidence that the Arabidopsis lead gene functions in soybean to enhance tolerance to nitrogen deprivation (increased nitrogen tolerance).

Soybean plants transformed with validated genes can be assayed to study agronomic characteristics relative to control or reference plants. For example, yield enhancement and/or stability under low and high nitrogen conditions (e.g., nitrogen limiting conditions and nitrogen-sufficient conditions) can be assayed.

Example 11 Transformation of Maize with Validated Arabidopsis Lead Genes Using Particle Bombardment

Maize plants can be transformed to overexpress a validated Arabidopsis lead gene or the corresponding homologs from various species in order to examine the resulting phenotype.

The same GATEWAY® entry clones described in Example 5 can be used to directionally clone each respective gene into a maize transformation vector. Expression of the gene in the maize transformation vector can be under control of a constitutive promoter such as the maize ubiquitin promoter (Christensen et al., Plant Mol. Biol. 12:619-632 (1989) and Christensen et al., Plant Mol. Biol. 18:675-689 (1992))

The recombinant DNA construct described above can then be introduced into maize cells by particle bombardment. Techniques for corn transformation by particle bombardment have been described in International Patent Publication WO 2009/006276, the contents of which are herein incorporated by reference.

T1 plants can be grown under nitrogen limiting conditions, for example, 1 mM nitrate, and analyzed for phenotypic changes. The following parameters can be quantified using image analysis: plant area, volume, growth rate and color analysis can be collected and quantified. Overexpression constructs that result in an alteration, compared to suitable control plants, in greenness (green color bin), yield, growth rate, biomass, fresh or dry weight at maturation, fruit or seed yield, total plant nitrogen content, fruit or seed nitrogen content, nitrogen content in vegetative tissue, free amino acid content in the whole plant, free amino acid content in vegetative tissue, free amino acid content in the fruit or seed, protein content in the fruit or seed, or protein content in a vegetative tissue can be considered evidence that the Arabidopsis lead gene functions in maize to enhance tolerance to nitrogen deprivation (increased nitrogen tolerance).

Example 12 Electroporation of Agrobacterium tumefaciens LBA4404

Electroporation competent cells (40 μL), such as Agrobacterium tumefaciens LBA4404 (containing PHP10523), are thawed on ice (20-30 min). PHP10523 contains VIR genes for T-DNA transfer, an Agrobacterium low copy number plasmid origin of replication, a tetracycline resistance gene, and a Cos site for in vivo DNA bimolecular recombination. Meanwhile the electroporation cuvette is chilled on ice. The electroporator settings are adjusted to 2.1 kV. A DNA aliquot (0.5 μL parental DNA at a concentration of 0.2 μg-1.0 μg in low salt buffer or twice distilled H₂O) is mixed with the thawed Agrobacterium tumefaciens LBA4404 cells while still on ice. The mixture is transferred to the bottom of electroporation cuvette and kept at rest on ice for 1-2 min. The cells are electroporated (Eppendorf electroporator 2510) by pushing the “pulse” button twice (ideally achieving a 4.0 millisecond pulse). Subsequently, 0.5 mL of room temperature 2×YT medium (or SOC medium) are added to the cuvette and transferred to a 15 mL snap-cap tube (e.g., FALCON™ tube). The cells are incubated at 28-30° C., 200-250 rpm for 3 h.

Aliquots of 250 μL are spread onto plates containing YM medium and 50 μg/mL spectinomycin and incubated three days at 28-30° C. To increase the number of transformants one of two optional steps can be performed:

Option 1: Overlay plates with 30 μL of 15 mg/mL rifampicin. LBA4404 has a chromosomal resistance gene for rifampicin. This additional selection eliminates some contaminating colonies observed when using poorer preparations of LBA4404 competent cells.

Option 2: Perform two replicates of the electroporation to compensate for poorer electrocompetent cells.

Identification of Transformants:

Four independent colonies are picked and streaked on plates containing AB minimal medium and 50 μg/mL spectinomycin for isolation of single colonies. The plates are incubated at 28° C. for two to three days. A single colony for each putative cointegrate is picked and inoculated with 4 mL of 10 g/L bactopeptone, 10 g/L yeast extract, 5 g/L sodium chloride, and 50 mg/L spectinomycin. The mixture is incubated for 24 h at 28° C. with shaking. Plasmid DNA from 4 mL of culture is isolated using QIAGEN Miniprep and an optional Buffer PB wash. The DNA is eluted in 30 μL. Aliquots of 2 μL are used to electroporate 20 μL of DH10b+20 μL of twice distilled H₂O as per above. Optionally a 15 μL aliquot can be used to transform 75-100 μL of INVITROGEN™ Library Efficiency DH5a. The cells are spread on plates containing LB medium and 50 μg/mL spectinomycin and incubated at 37° C. overnight.

Three to four independent colonies are picked for each putative cointegrate and inoculated 4 mL of 2×YT medium (10 g/L bactopeptone, 10 g/L yeast extract, 5 g/L sodium chloride) with 50 μg/mL spectinomycin. The cells are incubated at 37° C. overnight with shaking. Next, the plasmid DNA is isolated from 4 mL of culture using QIAprep® Miniprep with optional Buffer PB wash (elute in 50 μL). 8 μL are used for digestion with SalI (using parental DNA and PHP10523 as controls). Three more digestions using restriction enzymes BamHI, EcoRI, and HindIII are performed for 4 plasmids that represent 2 putative cointegrates with correct SalI digestion pattern (using parental DNA and PHP10523 as controls). Electronic gels are recommended for comparison.

Example 13 Transformation of Maize Using Agrobacterium

Maize plants can be transformed to overexpress a validated Arabidopsis lead gene or the corresponding homologs from various species in order to examine the resulting phenotype.

Agrobacterium-mediated transformation of maize is performed essentially as described by Zhao et al., in Meth. Mol. Biol. 318:315-323 (2006) (see also Zhao et al., Mol. Breed. 8:323-333 (2001) and U.S. Pat. No. 5,981,840 issued Nov. 9, 1999, incorporated herein by reference). The transformation process involves bacterium inoculation, co-cultivation, resting, selection, and plant regeneration.

1. Immature Embryo Preparation:

Immature maize embryos are dissected from caryopses and placed in a 2 mL microtube containing 2 mL PHI-A medium.

2. Agrobacterium Infection and Co-Cultivation of Immature Embryos: 2.1 Infection Step:

PHI-A medium of (1) is removed with 1 mL micropipettor, and 1 mL of Agrobacterium suspension is added. The tube is gently inverted to mix. The mixture is incubated for 5 min at room temperature.

2.2 Co-Culture Step:

The Agrobacterium suspension is removed from the infection step with a 1 mL micropipettor. Using a sterile spatula the embryos are scraped from the tube and transferred to a plate of PHI-B medium in a 100×15 mm Petri dish. The embryos are oriented with the embryonic axis down on the surface of the medium. Plates with the embryos are cultured at 20° C., in darkness, for three days. L-Cysteine can be used in the co-cultivation phase. With the standard binary vector, the co-cultivation medium supplied with 100-400 mg/L L-cysteine is critical for recovering stable transgenic events.

3. Selection of Putative Transgenic Events:

To each plate of PHI-D medium in a 100×15 mm Petri dish, 10 embryos are transferred, maintaining orientation, and the dishes are sealed with parafilm. The plates are incubated in darkness at 28° C. Actively growing putative events, evinced as pale yellow embryonic tissue, are expected to be visible in six to eight weeks. Embryos that produce no events may be brown and necrotic, and little friable tissue growth is evident. Putative transgenic embryonic tissue is subcultured to fresh PHI-D plates at two-three week intervals, depending on growth rate. The events are recorded.

4. Regeneration of T0 Plants:

Embryonic tissue propagated on PHI-D medium is subcultured to PHI-E medium (somatic embryo maturation medium), in 100×25 mm Petri dishes and incubated at 28° C., in darkness, until somatic embryos mature, for about ten to eighteen days. Individual, matured somatic embryos with well-defined scutellum and coleoptile are transferred to PHI-F embryo germination medium and incubated at 28° C. in the light (about 80 μE from cool white or equivalent fluorescent lamps). In seven to ten days, regenerated plants, about 10 cm tall, are potted in horticultural mix and hardened-off using standard horticultural methods.

Media for Plant Transformation:

-   -   1. PHI-A: 4 g/L CHU basal salts, 1.0 mL/L 1000× Eriksson's         vitamin mix, 0.5 mg/L thiamin HCl, 1.5 mg/L 2,4-D, 0.69 g/L         L-proline, 68.5 g/L sucrose, 36 g/L glucose, pH 5.2. Add 100 μM         acetosyringone (filter-sterilized).     -   2. PHI-B: PHI-A without glucose, increase 2,4-D to 2 mg/L,         reduce sucrose to 30 g/L and supplemented with 0.85 mg/L silver         nitrate (filter-sterilized), 3.0 g/L GELRITE®, 100 μM         acetosyringone (filter-sterilized), pH 5.8.     -   3. PHI-C: PHI-B without GELRITE® and acetosyringonee, reduce         2,4-D to 1.5 mg/L and supplemented with 8.0 g/L agar, 0.5 g/L         2-[N-morpholino]ethane-sulfonic acid (MES) buffer, 100 mg/L         carbenicillin (filter-sterilized).     -   4. PHI-D: PHI-C supplemented with 3 mg/L bialaphos         (filter-sterilized).     -   5. PHI-E: 4.3 g/L of Murashige and Skoog (MS) salts, (GIBCO, BRL         11117-074), 0.5 mg/L nicotinic acid, 0.1 mg/L thiamine HCl, 0.5         mg/L pyridoxine HCl, 2.0 mg/L glycine, 0.1 g/L myo-inositol, 0.5         mg/L zeatin (Sigma, Cat. No. Z-0164), 1 mg/L indole acetic acid         (IAA), 26.4 μg/L abscisic acid (ABA), 60 g/L sucrose, 3 mg/L         bialaphos (filter-sterilized), 100 mg/L carbenicillin         (filter-sterilized), 8 g/L agar, pH 5.6.     -   6. PHI-F: PHI-E without zeatin, IAA, ABA; reduce sucrose to 40         g/L; replacing agar with 1.5 g/L GELRITE®; pH 5.6.

Plants can be regenerated from the transgenic callus by first transferring clusters of tissue to N6 medium supplemented with 0.2 mg per liter of 2,4-D. After two weeks the tissue can be transferred to regeneration medium (Fromm et al., Bio/Technology 8:833-839 (1990)).

Transgenic T0 plants can be regenerated and their phenotype determined. T1 seed can be collected.

Furthermore, a recombinant DNA construct containing a validated Arabidopsis gene can be introduced into a maize inbred line either by direct transformation or introgression from a separately transformed line.

Transgenic plants, either inbred or hybrid, can undergo more vigorous field-based experiments to study yield enhancement and/or stability under nitrogen limiting and nitrogen non-limiting conditions.

Subsequent yield analysis can be done to determine whether plants that contain the validated Arabidopsis lead gene have an improvement in yield performance (under nitrogen limiting or non-limiting conditions), when compared to the control (or reference) plants that do not contain the validated Arabidopsis lead gene. Plants containing the validated Arabidopsis lead gene would have less yield loss relative to the control plants, for example, at least 25% less yield loss, under nitrogen limiting conditions, or would have increased yield relative to the control plants under nitrogen non-limiting conditions.

Example 14A Preparation of Expression Vector for Transformation of Maize Lines with Validated Candidate Arabidopsis Gene (At1g61140) Using Agrobacterium

Using the INVITROGEN™ GATEWAY® technology, an LR Recombination Reaction was performed with the GATEWAY® entry clone containing the sequence that encodes the Arabidopsis SNF2 domain-containing protein (described in Example 5 and referred to in this and subsequent examples as AT-SNF2.1), entry clone PHP23112 (SEQ ID NO:14), entry clone PHP20234 (SEQ ID NO:9; FIG. 9) and destination vector PHP22655 (SEQ ID NO:10) to generate the precursor plasmid PHP29872. PHP29872 contains the following expression cassettes:

1. Ubiquitin promoter::moPAT::PinII terminator cassette expressing the PAT herbicide resistance gene used for selection during the transformation process.

2. LTP2 promoter::DS-RED2::PinII terminator cassette expressing the DS-RED color marker gene used for seed sorting.

3. Ubiquitin promoter::AT-SNF2.1::PinII terminator cassette overexpressing the Arabidopsis SNF2.1 domain-containing protein (At1g61140.1).

Example 14B Transformation of Maize Lines with Validated Candidate Arabidopsis Gene (At1g61140) Using Agrobacterium

The SNF2.1 expression cassette present in vector PHP29872 (described in Example 14A) or vectors containing either of the other two At1g61140 variants can be introduced into a maize inbred line, or a transformable maize line derived from an elite maize inbred line, using Agrobacterium-mediated transformation as described in Examples 12 and 13.

Expression vector PHP29872 can be electroporated into the LBA4404 Agrobacterium strain containing vector PHP10523 (SEQ ID NO:7, FIG. 7) to create the co-integrate vector PHP29875, which contains the SNF2.1 expression cassette. The co-integrate vector is formed by recombination of the two plasmids, PHP29872 and PHP10523, through the COS recombination sites contained on each vector and contains the same three expression cassettes as above (Example 14A) in addition to other genes (TET, TET, TRFA, ORI terminator, CTL, ORI V, VIR C1, VIR C2, VIR G, VIR B) needed for the Agrobacterium strain and the Agrobacterium-mediated transformation. The electroporation protocol in, but not limited to, Example 12 may be used.

Example 15 Preparation of the Destination Vector PHP23236 for Transformation into Gaspe Flint Derived Maize Lines

Destination vector PHP23236 (FIG. 6; SEQ ID NO:6) was obtained by transformation of Agrobacterium strain LBA4404 containing PHP10523 (FIG. 7; SEQ ID NO:7) with vector PHP23235 (FIG. 8; SEQ ID NO:8) and isolation of the resulting co-integration product.

Destination vector PHP23236 can be used in a recombination reaction with an entry clone, as described in Example 16, to create a maize expression vector for transformation of Gaspe Flint derived maize lines.

Example 16 Preparation of Expression Constructs for Transformation into Gaspe Flint Derived Maize Lines

Using the INVITROGEN™ GATEWAY® LR Recombination technology, the same entry clone described in Example 5 can be directionally cloned into the destination vector PHP29634 (SEQ ID NO:15; FIG. 11) to create an expression vector. Destination vector PHP29634 is similar to destination vector PHP23236, however, destination vector PHP29634 has site-specific recombination sites FRT1 and FRT87 and also encodes the GAT4602 selectable marker protein for selection of transformants using glyphosate. The expression vector would contain the cDNA of interest, encoding either At-SNF2.1, At-SNF2.2, or AtSNF2.3, under control of the UBI promoter and is a T-DNA binary vector for Agrobacterium-mediated transformation into corn as described, but not limited to, the examples described herein.

Example 17A Transformation of Gaspe Flint Derived Maize Lines with Validated Candidate Arabidopsis Gene (At1g61140)

Maize plants can be transformed to overexpress the Arabidopsis At1g61140 gene (and the corresponding homologs from other species) in order to examine the resulting phenotype. Expression constructs such as the one described in Example 16 may be used.

Recipient Plants

Recipient plant cells can be from a uniform maize line having a short life cycle (“fast cycling”), a reduced size, and high transformation potential. Typical of these plant cells for maize are plant cells from any of the publicly available Gaspe Flint (GF) line varieties. One possible candidate plant line variety is the F1 hybrid of GF×QTM (Quick Turnaround Maize, a publicly available form of Gaspe Flint selected for growth under greenhouse conditions) disclosed in Tomes et al. (U.S. application Ser. No. 10/367,416 filed Feb. 13, 2003; U.S. Patent Publication No. 2003/0221212 A1 published Nov. 27, 2003). Transgenic plants obtained from this line are of such a reduced size that they can be grown in four inch pots (¼ the space needed for a normal sized maize plant) and mature in less than 2.5 months. (Traditionally 3.5 months is required to obtain transgenic T0 seed once the transgenic plants are acclimated to the greenhouse.) Another suitable line includes but is not limited to a double haploid line of GS3 (a highly transformable line)×Gaspe Flint. Yet another suitable line is a transformable elite maize inbred line carrying a transgene which causes early flowering, reduced stature, or both.

Transformation Protocol

Any suitable method may be used to introduce the transgenes into the maize cells, including but not limited to inoculation type procedures using Agrobacterium based vectors (see, for example, Examples 12 and 13). Transformation may be performed on immature embryos of the recipient (target) plant.

Precision Growth and Plant Tracking

The event population of transgenic (T0) plants resulting from the transformed maize embryos is grown in a controlled greenhouse environment using a modified randomized block design to reduce or eliminate environmental error. A randomized block design is a plant layout in which the experimental plants are divided into groups (e.g., thirty plants per group), referred to as blocks, and each plant is randomly assigned a location within the block.

For a group of thirty plants, twenty-four transformed, experimental plants and six control plants (plants with a set phenotype) (collectively, a “replicate group”) are placed in pots which are arranged in an array (a.k.a. a replicate group or block) on a table located inside a greenhouse. Each plant, control or experimental, is randomly assigned to a location within the block which is mapped to a unique, physical greenhouse location as well as to the replicate group. Multiple replicate groups of thirty plants each may be grown in the same greenhouse in a single experiment. The layout (arrangement) of the replicate groups should be determined to minimize space requirements as well as environmental effects within the greenhouse. Such a layout may be referred to as a compressed greenhouse layout.

An alternative to the addition of a specific control group is to identify those transgenic plants that do not express the gene of interest. A variety of techniques such as RT-PCR can be applied to quantitatively assess the expression level of the introduced gene. T0 plants that do not express the transgene can be compared to those which do.

Each plant in the event population is identified and tracked throughout the evaluation process, and the data gathered from that plant is automatically associated with that plant so that the gathered data can be associated with the transgene carried by the plant. For example, each plant container can have a machine readable label (such as a Universal Product Code (UPC) bar code) which includes information about the plant identity, which in turn is correlated to a greenhouse location so that data obtained from the plant can be automatically associated with that plant.

Alternatively any efficient, machine readable, plant identification system can be used, such as two-dimensional matrix codes or even radio frequency identification tags (RFID) in which the data is received and interpreted by a radio frequency receiver/processor. See U.S. application Ser. No. 10/324,288 filed Dec. 19, 2002 (U.S. Patent Publication No. 2004/0122592 A1 published Jun. 24, 2004), incorporated herein by reference.

Phenotypic Analysis Using Three-Dimensional Imaging

Each greenhouse plant in the T0 event population, including any control plants, is analyzed for agronomic characteristics of interest, and the agronomic data for each plant is recorded or stored in a manner so that it is associated with the identifying data (see above) for that plant. Confirmation of a phenotype (gene effect) can be accomplished in the T1 generation with a similar experimental design to that described above.

The T0 plants are analyzed at the phenotypic level using quantitative, non-destructive imaging technology throughout the plant's entire greenhouse life cycle to assess the traits of interest. Optionally, a digital imaging analyzer is used for automatic multi-dimensional analyzing of total plants. The imaging may be done inside the greenhouse. Two camera systems, located at the top and side, and an apparatus to rotate the plant, are used to view and image plants from all sides. Images are acquired from the top, front and side of each plant. All three images together provide sufficient information to evaluate, for example, the biomass, size, and morphology of each plant.

Due to the change in size of the plants from the time the first leaf appears from the soil to the time the plants are at the end of their development, the early stages of plant development are optionally documented with a higher magnification from the top. This imaging may be accomplished by using a motorized zoom lens system that is fully controlled by the imaging software.

In a single imaging analysis operation, the following events occur: (1) the plant is conveyed inside the analyzer area, rotated 360 degrees so its machine readable label can be read, and left at rest until its leaves stop moving; (2) the side image is taken and entered into a database; (3) the plant is rotated 90 degrees and again left at rest until its leaves stop moving, and (4) the plant is transported out of the analyzer.

Plants are allowed at least six hours of darkness per twenty four hour period in order to have a normal day/night cycle.

Imaging Instrumentation

Any suitable imaging instrumentation may be used, including but not limited to light spectrum digital imaging instrumentation commercially available from LemnaTec GmbH of Wurselen, Germany. The images are taken and analyzed with a LemnaTec Scanalyzer HTS LT-0001-2 having a ½″ IT Progressive Scan IEE CCD imaging device. The imaging cameras may be equipped with a motor zoom, motor aperture, and motor focus. All camera settings may be made using LemnaTec software. Optionally, the instrumental variance of the imaging analyzer is less than about 5% for major components and less than about 10% for minor components.

Software

The imaging analysis system comprises a LemnaTec HTS Bonit software program for color and architecture analysis and a server database for storing data from about 500,000 analyses, including the analysis dates. The original images and the analyzed images are stored together to allow the user to do as much reanalyzing as desired. The database can be connected to the imaging hardware for automatic data collection and storage. A variety of commercially available software systems (e.g., Matlab, others) can be used for quantitative interpretation of the imaging data, and any of these software systems can be applied to the image data set.

Conveyor System

A conveyor system with a plant rotating device may be used to transport the plants to the imaging area and rotate them during imaging. For example, up to four plants, each with a maximum height of 1.5 m, are loaded onto cars that travel over the circulating conveyor system and through the imaging measurement area. In this case the total footprint of the unit (imaging analyzer and conveyor loop) is about 5 m×5 m.

The conveyor system can be enlarged to accommodate more plants at a time. The plants are transported along the conveyor loop to the imaging area and are analyzed for up to 50 seconds per plant. Three views of the plant are taken. The conveyor system, as well as the imaging equipment, should be capable of being used in greenhouse environmental conditions.

Illumination

Any suitable mode of illumination may be used for the image acquisition. For example, a top light above a black background can be used. Alternatively, a combination of top- and backlight using a white background can be used. The illuminated area should be housed to ensure constant illumination conditions. The housing should be longer than the measurement area so that constant light conditions prevail without requiring the opening and closing or doors. Alternatively, the illumination can be varied to cause excitation of either transgene (e.g., green fluorescent protein (GFP), red fluorescent protein (RFP)) or endogenous (e.g. Chlorophyll) fluorophores).

Biomass Estimation Based on Three-Dimensional Imaging

For best estimation of biomass the plant images should be taken from at least three axes, optionally the top and two side (sides 1 and 2) views. These images are then analyzed to separate the plant from the background, pot and pollen control bag (if applicable). The volume of the plant can be estimated by the calculation:

Volume(voxels)=√{square root over (TopArea(pixels))}×√{square root over (Side1Area(pixels))}×√{square root over (Side2Area(pixels))}

In the equation above the units of volume and area are “arbitrary units”. Arbitrary units are entirely sufficient to detect gene effects on plant size and growth in this system because what is desired is to detect differences (both positive-larger and negative-smaller) from the experimental mean, or control mean. The arbitrary units of size (e.g. area) may be trivially converted to physical measurements by the addition of a physical reference to the imaging process. For instance, a physical reference of known area can be included in both top and side imaging processes. Based on the area of these physical references a conversion factor can be determined to allow conversion from pixels to a unit of area such as square centimeters (cm²). The physical reference may or may not be an independent sample. For instance, the pot, with a known diameter and height, could serve as an adequate physical reference.

Color Classification

The imaging technology may also be used to determine plant color and to assign plant colors to various color classes. The assignment of image colors to color classes is an inherent feature of the LemnaTec software. With other image analysis software systems color classification may be determined by a variety of computational approaches.

For the determination of plant size and growth parameters, a useful classification scheme is to define a simple color scheme including two or three shades of green (for example, hues 50-66, see FIG. 13) and, in addition, a color class for chlorosis, necrosis and bleaching, should these conditions occur. A background color class which includes non plant colors in the image (for example pot and soil colors) is also used and these pixels are specifically excluded from the determination of size. The plants are analyzed under controlled constant illumination so that any change within one plant over time, or between plants or different batches of plants (e.g. seasonal differences) can be quantified.

In addition to its usefulness in determining plant size growth, color classification can be used to assess other yield component traits. For these other yield component traits additional color classification schemes may be used. For instance, the trait known as “staygreen”, which has been associated with improvements in yield, may be assessed by a color classification that separates shades of green from shades of yellow and brown (which are indicative of senescing tissues). By applying this color classification to images taken toward the end of the T0 or T1 plants' life cycle, plants that have increased amounts of green colors relative to yellow and brown colors (expressed, for instance, as Green/Yellow Ratio) may be identified. Plants with a significant difference in this Green/Yellow ratio can be identified as carrying transgenes which impact this important agronomic trait.

The skilled plant biologist will recognize that other plant colors arise which can indicate plant health or stress response (for instance anthocyanins), and that other color classification schemes can provide further measures of gene action in traits related to these responses.

Plant Architecture Analysis

Transgenes which modify plant architecture parameters may also be identified using the present invention, including such parameters as maximum height and width, internodal distances, angle between leaves and stem, number of leaves starting at nodes, and leaf length. The LemnaTec system software may be used to determine plant architecture as follows. The plant is reduced to its main geometric architecture in a first imaging step and then, based on this image, parameterized identification of the different architecture parameters can be performed. Transgenes that modify any of these architecture parameters either singly or in combination can be identified by applying the statistical approaches previously described.

Pollen Shed Date

Pollen shed date is an important parameter to be analyzed in a transformed plant, and may be determined by the first appearance on the plant of an active male flower. To find the male flower object, the upper end of the stem is classified by color to detect yellow or violet anthers. This color classification analysis is then used to define an active flower, which in turn can be used to calculate pollen shed date.

Alternatively, pollen shed date and other easily visually detected plant attributes (e.g., pollination date, first silk date) can be recorded by the personnel responsible for performing plant care. To maximize data integrity and process efficiency, this data is tracked by utilizing the same barcodes utilized by the LemnaTec light spectrum digital analyzing device. A computer with a barcode reader, a palm device, or a notebook PC may be used for ease of data capture recording time of observation, plant identifier, and the operator who captured the data.

Orientation of the Plants

Mature maize plants grown at densities approximating commercial planting often have a planar architecture. That is, the plant has a clearly discernable broad side, and a narrow side. The image of the plant from the broadside is determined. To each plant a well defined basic orientation is assigned to obtain the maximum difference between the broadside and edgewise images. The top image is used to determine the main axis of the plant, and an additional rotating device is used to turn the plant to the appropriate orientation prior to starting the main image acquisition.

Example 17B Transformation of Gaspe Flint Derived Maize Lines with a Maize Homolog

Using the INVITROGEN™ GATEWAY® LR Recombination technology, entry clones may be created for any of the maize homologs (SEQ ID NO:18/19, 20/21, 22/23, 43/44, or 45/46) (see Example 5 for entry clone preparation) and can be directionally cloned into the GATEWAY® destination vector 29634 (SEQ ID NO:15; FIG. 11) to create corresponding expression vectors. Each expression vector would contain the cDNA of interest under control of the UBI promoter and would be a T-DNA binary for Agrobacterium-mediated transformation into maize as described, but not limited to, the examples described herein.

Example 18 Screening of Maize Lines Under Nitrogen Limiting Conditions

Gaspe Flint Derived Maize Lines

Transgenic plants can contain two or three doses of Gaspe Flint-3 with one dose of GS3 (GS3/(Gaspe-3)2× or GS3/(Gaspe-3)3×) and segregate 1:1 for a dominant transgene. Transgenic plants can be planted in 100% Turface, a commercial potting medium, and can be watered four times each day with 1 mM KNO₃ growth medium and with 2 mM KNO₃, or higher, growth medium (see FIG. 14). Control plants grown in 1 mM KNO₃ medium would be less green, produce less biomass and have a smaller ear at anthesis (see FIG. 15 for an illustration of sample data). Gaspe-derived lines would be grown to the flowering stage.

Statistics would be used to decide if differences seen between treatments are really different. FIG. 15 illustrates one method which places letters after the values. Those values in the same column that have the same letter (not group of letters) following them are not significantly different. Using this method, if there are no letters following the values in a column, then there are no significant differences between any of the values in that column or, in other words, all the values in that column are equal.

Expression of a transgene would result in plants with improved plant growth in 1 mM KNO₃ when compared to a transgenic null. Thus biomass and greenness (as described in Examples 2 and 17A) would be monitored during growth and compared to a transgenic null. Improvements in growth, greenness and ear size at anthesis would be indications of increased nitrogen tolerance.

Seedling Assay

Transgenic maize plants can also be evaluated using a seedling assay that assesses plant performance under nitrogen limiting conditions. In an 18 day seedling assay, for example, transgenic plants are planted in Turface, a commercial potting medium, and then watered four times each day with a solution containing the following nutrients: 1 mM CaCl₂, 2 mM MgSO₄, 0.5 mM KH₂PO₄, 83 ppm Sprint330, 3 mM KCl, 1 mM KNO₃, 1 μM ZnSO₄, 1 μM MnCl₂, 3 μM H₃BO₄, 0.1 μM CuSO₄, and 0.1 μM NaMoO₄. Plants are harvested 18 days after planting, and a number of traits are assessed, including but not limited to: SPAD (greenness), stem diameter, root dry weight, shoot dry weight, total dry weight, mg Nitrogen per grams of dry weight (mg N/g dwt), and plant N concentration. Means are compared to null mean parameters using a Student's t test with a minimum (P<t) of 0.1.

Example 19 Nitrogen Utilization Efficiency Seedling Assay

Seed of transgenic events were separated into Transgenic (Treatment 1; contain construct PHP29875) and Null (Treatment 2) seed using a seed color marker.

Treatments (Transgenic or Bulked Null) were each randomly assigned to blocks of 54 pots (experimental units) arranged in 6 rows by 9 columns. Each treatment (Transgenic or Bulked Nulls) was replicated 9 times.

All seeds were planted in 4 inch, square pots containing Turface on 8 inch, staggered centers and watered four times each day with a solution containing the following nutrients:

1 mM CaCl₂ 2 mM MgSO₄ 0.5 mM KH₂PO₄  83 ppm Sprint330 3 mM KCl 1 mM KNO₃   1 μM ZnSO₄   1 μM MnCl₂ 3 μM H₃BO₄ 1 μM MnCl₂ 0.1 μM CuSO₄ 0.1 μM NaMoO₄ After emergence the plants were thinned to one seed per pot. At harvest, plants were removed from the pots, and the Turface was washed from the roots. The roots were separated from the shoot, placed in a paper bag, and dried at 70° C. for 70 hr. The dried plant parts (roots and shoots) were weighed and placed in a 50 ml conical tube with approximately 20 5/32 inch steel balls and then ground by shaking in a paint shaker.

The Nitrogen/Protein Analyzer from Thermo Electron Corporation (model FlashEA 1112 N) uses approximately 30 mg of the ground tissue. A sample is dropped from the Autosampler into the crucible inside the oxidation reactor chamber. At 900° C. and pure oxygen, the sample is oxidized by a strong exothermic reaction creating a gas mixture of N₂, CO₂, H₂O, and SO₂. After the combustion is complete, the carrier gas helium is turned on and the gas mixture flows into the reduction reaction chamber. At 680° C., the gas mixture flows across the reduction copper where nitrogen oxides possibly formed are converted into elemental nitrogen and the oxygen excess is retained. From the reduction reactor, the gas mixture flows across a series of two absorption filters. The first filter contains soda lime and retains carbon and sulfur dioxides. The second filter contains molecular sieves and granular silica gel to hold back water. Nitrogen is then eluted in the chromatographic column and conveyed to the thermal conductivity detector that generates an electrical signal, which, properly processed by the Eager 300 software, provides the nitrogen-protein percentage.

Using these data, the following parameters were measured and means of Transgenic parameters were compared to means of Null parameters using a Student's t test:

Total Plant Biomass (total dwt (g)) Root Biomass (root dwt (g)) Shoot Biomass (shoot dwt (g)) Root/Shoot Ratio (root:shoot dwt ratio) Plant N concentration (mg N/g dwt) Total Plant N (total N (mg))

Variance was calculated within each block using an Analysis of Variance (ANOVA) calculation and a completely random design (CRD) model. An overall treatment effect for each block was calculated using an F statistic by dividing overall block treatment mean square by the overall block error mean square. The probability of a greater Student's t test was calculated for each transgenic mean compared to the appropriate null. Variables that show a significant difference (*) have a minimum (P<t) of 0.1.

Table 5 shows the raw data and the two tailed Student's t probability for plants containing construct PHP29875. The mathematical sign of the p value reflects the relative performance of the event vs. the corresponding null, i.e. ‘+’=increased performance, ‘−’=decreased performance. Comparisons were made between the transgenic events and construct nulls. A construct null is a negative entry that is made up of a sampling of kernels from the negative segregants and is therefore a representative sample of all negatives.

TABLE 5 Greenhouse Seedling Assay Data for PHP29875 Planting date Event Name Mean Null t Test Mean Null t Test root dwt (g) shoot dwt (g) Aug. 11, 2008 E7733.53.2.2 0.769 0.758 0.851 1.350 1.342 0.948 Aug. 11, 2008 E7733.53.2.4 0.811 0.758 0.383 1.426 1.342 0.496 Aug. 11, 2008 E7733.53.2.7.a 0.830 0.758 0.227 1.520 1.342 0.141 Aug. 11, 2008 E7733.53.2.7.b 0.833 0.758 0.206 1.529 1.342 0.123 Aug. 11, 2008 E7733.53.3.13 0.803 0.758 0.444 1.421 1.342 0.510 Sep. 2, 2009 E7733.53.2.19 0.778 0.776 0.963 1.360 1.330 0.756 Sep. 2, 2009 E7733.53.2.2 0.800 0.776 0.607 1.366 1.330 0.713 Sep. 2, 2009 E7733.53.2.20 0.781 0.776 0.907 1.350 1.330 0.836 Sep. 2, 2009 E7733.53.2.25 0.728 0.776 −0.316 1.286 1.330 −0.646 Sep. 2, 2009 E7733.53.2.4 0.706 0.776 −0.144 1.204 1.330 −0.197 total dwt (g) root:shoot dwt ratio Aug. 11, 2008 E7733.53.2.2 2.119 2.100 0.913 0.575 0.569 0.798 Aug. 11, 2008 E7733.53.2.4 2.238 2.100 0.444 0.571 0.569 0.919 Aug. 11, 2008 E7733.53.2.7.a 2.350 2.100 0.155 0.552 0.569 0.445 Aug. 11, 2008 E7733.53.2.7.b 2.362 2.100 0.136 0.546 0.569 0.314 Aug. 11, 2008 E7733.53.3.13 2.224 2.100 0.475 0.567 0.569 0.918 Sep. 2, 2009 E7733.53.2.19 2.138 2.106 0.816 0.577 0.583 −0.829 Sep. 2, 2009 E7733.53.2.2 2.166 2.106 0.665 0.593 0.583 0.707 Sep. 2, 2009 E7733.53.2.20 2.131 2.106 0.854 0.581 0.583 −0.963 Sep. 2, 2009 E7733.53.2.25 2.013 2.106 −0.507 0.568 0.583 −0.587 Sep. 2, 2009 E7733.53.2.4 1.910 2.106 −0.163 0.596 0.583 0.638 mg N/g dwt total N (mg) Aug. 11, 2008 E7733.53.2.2 29.700 26.800 0.265 39.638 35.542 0.284 Aug. 11, 2008 E7733.53.2.4 24.813 26.800 0.457 34.457 35.542 0.782 Aug. 11, 2008 E7733.53.2.7.a 24.878 26.800 0.458 37.938 35.542 0.529 Aug. 11, 2008 E7733.53.2.7.b 25.844 26.800 0.712 39.253 35.542 0.331 Aug. 11, 2008 E7733.53.3.13 25.278 26.800 0.557 34.949 35.542 0.876 Sep. 2, 2009 E7733.53.2.19 21.722 21.756 −0.971 29.197 28.759 0.791 Sep. 2, 2009 E7733.53.2.2 22.289 21.756 0.564 30.363 28.759 0.334 Sep. 2, 2009 E7733.53.2.20 22.922 21.756 0.210 30.644 28.759 0.257 Sep. 2, 2009 E7733.53.2.25 23.000 21.756 0.181 29.289 28.759 0.748 Sep. 2, 2009 E7733.53.2.4 21.989 21.756 0.800 26.311 28.759 −0.143

Example 20A Yield Analysis of Maize Lines with the Arabidopsis Lead Genes or Maize Homologs

Transgenic plants, either inbreds or topeross hybrids, can undergo more vigorous field-based experiments to study yield enhancement and/or stability under nitrogen limiting and non-limiting conditions. A standardized yield trial will typically include 4 to 6 replications and at least 4 locations.

Yield analysis can be done to determine whether plants that contain the validated Arabidopsis gene that encodes a SNF2 domain-containing protein or a related maize gene have an improvement in yield performance (under nitrogen limiting or non-limiting conditions), when compared to the control (or reference) plants, that are either construct null or wild-type. Specifically, nitrogen limiting conditions can be imposed during the flowering and/or grain fill period for plants that contain either the validated Arabidopsis lead gene or a maize homolog of Int6 and the control plants. Reduction in yield can be measured for both. Plants containing the validated Arabidopsis lead gene or a maize homolog thereof would have less yield loss relative to the control plants, under nitrogen limiting conditions, or would have increased yield relative to the control plants under nitrogen non-limiting conditions.

Example 20B Yield Analysis of Maize Lines Transformed with PHP29875

Corn hybrid testcrosses, containing the Arabidopsis thaliana lead gene (encoding a SNF2 domain-containing polypeptide) expression cassette present in vector PHP29875, and their controls were grown in low nitrogen (LN) and normal nitrogen (NN) environments in 2008 and in 2009 at multiple locations. A low nitrogen (LN) environment consists of a less than normal amount of nitrogen fertilizer applied in early spring or summer, whereas a normal nitrogen (NN) environment consists of adding adequate nitrogen for normal yields, based on soil test standards established for specific growing areas by Federal and State Extension services. A yield reduction was observed in LN conditions as compared to that obtained in NN conditions. For the analysis, a construct null is a negative entry made up of negative segregants from all events within a construct, and a bulk null is a negative entry made up of all negative segregants from all constructs within an experiment.

Nine transgenic events were field tested in 2008 at two locations, York, Nebr. (YK) and Woodland, Calif. (WO), and yield was assessed. The corn hybrid testcrosses were compared to the construct nulls (CN). The results of the 2008 field test are presented in Table 6.

TABLE 6 2008 Field Tests of Maize Transformed with PHP29875 Event YK LN WOLN YK NN WONN CN 104 173 198 211 E7733.53.2.19 107 170 199 208 E7733.53.2.2 105 175 N/A 215 E7733.53.2.20 104 167 194 215 E7733.53.2.25 105 170 195 209 E7733.53.2.4 106 174 197 214 E7733.53.2.7 105 172 196 212 E7733.53.2.9 105 173 193 211 E7733.53.3.4 105 173 195 207 E7733.53.3.13 105 169 197 211

-   -   Unit of measure is bushels/acre.     -   Shading represents sig. higher (P<0.1) result compared to the         construct null (CN).     -   Bold represents sig. lower (P<0.1) result compared to the         construct null (CN).

Eight of the nine previously tested transgenic events were field tested in 2009 at the following locations: York, Nebr. (YK); Marion, Iowa (MR); Woodland, Calif. (WO); Dallas Center, Iowa (DS); and Princeton, Ind. (PR). However, in 2009, the corn hybrid testcrosses were compared to the bulk null (BN). The results of the 2009 field test are presented in Table 7. In York, under low nitrogen conditions, three events showed a significant increase in yield over the bulk null, and under normal nitrogen conditions, one event showed a significant increase in yield over the bulk null. In Woodland, under low nitrogen conditions, one event had significantly higher yields as compared to the bulk null. In Marion, under low nitrogen conditions, the yield for three events was significantly higher than the bulk null.

TABLE 7 2009 Field Tests of MaizeTransformed with PHP29875

Unit of measure is bushels/acre. Shading represents sig. higher (P < 0.1) result compared to the bulk null (BN). Bold represents sig. lower (P < 0.1) result compared to the bulk null (BN).

Example 21 Transformation and Evaluation of Soybean with Soybean Homologs of Validated Lead Genes

Based on homology searches, one or several candidate soybean homologs of validated Arabidopsis leads can be identified and also be assessed for their ability to enhance tolerance to nitrogen limiting conditions in soybean. Vector construction, plant transformation and phenotypic analysis will be similar to that in previously described Examples.

Example 22 Transformation and Evaluation of Maize with Maize Homologs of Validated Lead Genes

Based on homology searches, one or several candidate maize homologs of validated Arabidopsis lead genes can be identified (e.g., SEQ ID NOs:18/19, 20/21, 22/23, 43/44, or 45/46) and also be assessed for their ability to enhance tolerance to nitrogen limiting conditions in maize. Vector construction, plant transformation and phenotypic analysis can be similar to that in previously described Examples.

Example 23 Transformation of Arabidopsis with Maize and Soybean Homologs of Validated Lead Genes

Soybean and maize homologs to validated Arabidopsis lead genes can be transformed into Arabidopsis under control of the 35S promoter and assayed for leaf area and green color bin accumulation when grown on low nitrogen medium. Vector construction and plant transformation can be as described in the examples herein. Assay conditions, data capture and data analysis can be similar to that in previously described Examples. 

What is claimed is:
 1. A method of increasing nitrogen stress tolerance in a plant, comprising: (a) introducing into a regenerable plant cell a recombinant DNA construct comprising a polynucleotide operably linked to at least one regulatory sequence, wherein the polynucleotide encodes a polypeptide having an amino acid sequence of at least 95% sequence identity, based on the Clustal V method of alignment, when compared to SEQ ID NO:25; (b) regenerating a transgenic plant from the regenerable plant cell after step (a), wherein the transgenic plant comprises in its genome the recombinant DNA construct; and (c) obtaining a progeny plant derived from the transgenic plant, wherein said progeny plant comprises in its genome the recombinant DNA construct and exhibits increased nitrogen stress tolerance when compared to a control plant not comprising the recombinant DNA construct.
 2. The method of claim 1, wherein said plant is selected from the group consisting of: maize, soybean, sunflower, sorghum, canola, wheat, alfalfa, cotton, rice, barley, millet, sugar cane, and switchgrass. 